I hope that it isn't considered snakeposting if I divide 3 posts made by the same person about the same subject in order to answer them each in turn. If it does, I apologise in advance and I will correct it, but as they are different posts, I don't see why it would be snakeposting.
While this is true in general for a liege-vassal relationship, I disagree that it is true for Ling Qi's specific situation. The reason a vassal can't be compelled to do something like that is because in a feudal system the vassal has an established power base of their own. If Shenhua tried to force, for example, the Bao to make an alliance like that she'd have to deal with the fact they are strong enough to actually fight her. They'd likely get stomped if they tried but it would cost Shenhua to do it. So there are lines that both sides will not cross, but they only exist because they are backed up by force.
Ling Qi, in contrast, has no vassals, no clan members, no fief or significant income and no way to rectify that without Cai support. The power disparity means that Shenhua or CRX could force Ling Qi into a marriage if they really wanted to and were willing to bear the cost of alienating her. If they made getting a decent fief, help feeding Zhengui, and support for cultivation contingent on marrying someone of their choice Ling Qi's choices are to essentially give up on reaching the higher realms, go rogue, or give in. This could be handled quietly, but even if it got out and offended the other clans sensibilities it wouldn't matter. While they might not appreciate the move, no clan is going to burn political capital opposing the Cai for a new single cultivator clan.
First of all, in a cultivation world, one's foremost power base is their cultivation base. The reason Barons are given fiefs and there is an extensive system of cultivation social mobility is because people already have what, in universe, can be considered a power base. True, a green Baron without a family or soldiers has a weaker and shakier power base than the average Baro and a green or cyan could do nothing if Shenhua wanted them gone, I felt it was important to point out how differently power bases work in this universe to state that no, Ling Qi is not different than most Barons, in fact, when she reaches Cyan she'll have a stronger power base than most. (not necessarily a firmer one mind you, until family circumstances can be replicated even a ducal family is shaky... yes, I am stating that the Cais are hella shaky, as they may not outlive Shenhua.)
And this is exactly the powerbase that made CRX want to finance Ling Qi. CRX did not pick Ling Qi out of charity, she picked her because of her powerbase being exceptional among non established barons. The reason she goes overboard in financing her is exactly because she considers her valuable. So, to an extent, Ling Qi has a better negotiating position than most Barons because her powerbase seems better. At least, until/unless she starts to stall out in cultivation. Mind you, our liege still negotiates from a position of strength, but lieges always do so. The fact she gives us a lot means we are a good enough investment that ourloyalty is valuable, however, not that we are dependent on a charity she may withdraw at any point.
The issue is that Ling Qi is legally a vassal of the Cai, who are all about law and order, so she can't just leave to join a different clan without it being a threat to Shenhua's authority. If the Cai felt strongly enough about this hypothetical marriage that they were forcing Ling Qi to do it, with all the negatives that entails, they would certainly demand a lot in return for calling off their plans. I don't think it would be as simple as just paying the Cai off, and anyone with sense thinks very carefully about deliberately annoying a White cultivator, particularly one with Shenhua's reputation.
They could oppose it, kick up a bug fuss, and demand concessions later but, if Shenhua was determined, they couldn't stop it without directly challenging her right to manage her own vassals. To do that they'd really need a coalition of most of the Emerald Seas or outside ducal/imperial support which would have enormous consequences. I was a bit too broad in saying no one would burn political capital for Ling Qi, but there is no way it would be enough if Shenhua tried to force the issue.
Ling Qi is legally a vassal of CRX in particular, not the Cai in general. That is an important distinction. It means CRX has to punish us if we leave, not Shenhua, who likely wouldn't interfere and just jot that as a lack mark against CRX.
You are also understating how much noility cares about predecent. Forcing us to marry could kick up fuss even in different ducal famillies who want to reassure their vessels that no, they won't overreach like that, never mind just in Shenhua's province.
It would be an attack on Ling Qi's freedoms but very much an indirect attack on them at worst. I don't think this would be an abuse of power, at least not in Shenhua's eyes. As duke she has the power to distribute resources however she feels best helps the province, and if Ling Qi won't obey her on an important issue Shenhua will find some other use for those resources.
Again, Shenhua is not Ling Qi's liege, she is CRX's and the count clan's liege. Its CRX who would redistribute her resources, and I doubt she will do it unless she finds retainers more talented than Ling Qi because she is not in a position to, especially now that she has a sister.
All those things said, I still am loyal to CRX and do not think she'll force us to marry or that she is the kind of person that would violate vassal rights unless they result in blatant injustice. I am just saying that we aren't her pawn, or any chess piece for that matter, we are much closer to being one of her ministers compared to a high minister or a president, she has rank, power, money and control over us, but not really to an absolute extent, and we aren't big enough to jump ship and make it on our own, but we are big enough to jump on another ship if we maneuer correctly, allthough it would be assholish and somewhat perilous.
Edit:
As a retainer of the Cai, LQ is expected to do her utmost to help the Cai achieve their political and economic goals in exchange for the support they give to her and the Ling Clan. Since marriage is viewed by the Empire's nobility as a way to build a power base and advance political goals, it seems that this includes marrying a member of a suitable clan. This could be someone suggested by the Cai or someone that LQ finds on her own that the Cai approve of. If LQ refuses to marry a suitable candidate, I'd assume that Shenhua would no longer consider her retainer material and would reduce the amount of material and political support given to the Ling Clan accordingly. There's no need for Shenhua to piss off all of her vassals by forcing a marriage on LQ, she'll just quietly demote LQ from her retainer position and find another prodigy or loyal clan head who is willing to marry for politics in exchange for retainership. LQ isn't particularly special after all, she was just in the right place at the right time.
Retainers are not slaves or extentions of one's will, they are loyal enforcers and/or advisors. Not even elder Jiao had his marriage dictated by his liege, and he was much, much more loyal and close to him and married a political dead end (a spirit)
