i mean it's not like we can't social her without a soul link or somethin?
We can, yes, but that still leads to the fact that it might not necessarily foster her growth very much. She was
not designed at all to be a sapient lifeform with a soul. That she got one anyway is a small miracle--but she's going to be running into the problem that is "
a machine is a very shitty vessel for fostering the development of a soul|, she's not a shifter like the other guy is, she's naturally designed as a mechanoid from the ground up. It might happen, but it normally takes the better part of centuries for an object to acquire a spirit and sapience in their own right--she got it pretty much from activation--that kind of thing is only
rarely stable mythologically speaking, and usually leads to tragedy when it happens anyway.
Giving her the Contract gives her fuel needed to foster her growth properly, because it's being provided from the outside. It covers for the whole "Not being built as a living being, and thus, not designed to properly foster development of a mature spirit" issue by giving her energy from us.
That's the theory anyway.
Like I said, if we were some older and more mature wizard, I'd be more against this. We'd have more options in that case though. We're barely more mature than she is though, and one of our priorities is to learn about life. We'll have influence here--yes--but a Contracted Shikigami is not a slave--and she'll have influence right back as we can grow as people together.
I made the "Imouto Get!" Joke, but it's not actually inaccurate in this case.