I much prefer focusing on human Gods when talking about the daughters, but I guess I'll actually address the elf daughters idea now that we are moments away from getting books on the entire elf pantheon (barring a sudden upset in the vote).
The elf pantheon has nine female Goddesses. Three of them - Drakira, Ereth Khial, and Anath Raema - can be ruled out immediately as they are too comically evil to be Shallya's daughters. Two - Hekarti and Atharti - are actually known to be sisters, so they can be safely considered a package deal; either both are daughters, or neither are. Even aside from the fact that they don't resemble Ranald or Shallya at all, we can fairly confidently rule those two out as well because we interacted with Hekarti worshippers with the Father active - we recruited House Tindomiel the same turn we want to the Nordland Hedgewise, meaning that both the Tindomiel negotiations and our conversation with Sarvoi happened with the Father active. Some have argued that this doesn't necessarily disprove Hekarti being a daughter, because the head of house Tindomiel can have trust and faith in Mathilde and still be a jerk or whatever. I find this very unconvincing, and if this is your position then it's hard to see what sort of casual interaction with elf worshippers that could plausibly happen in Lothern could prove or disprove a daughter theory.
This leaves Morai-Heg, Isha, Lileath, and Ladrielle. Morai-Heg does not resemble Shallya or Ranald, except in the very weak sense that She resembles Morr and Morr is said to be Shallya's father, so I think it's pretty safe to say She is not a likely candidate. Isha resembles Shallya - in fact She so resembles Shallya that a common theory is that Isha is Shallya. Lileath is associated both with luck and with innocence and forgiveness, which does seem like it could fit a daughter of Ranald and Shallya. Ladrielle's aspects arguably resemble Ranald, but more importantly Ladrielle resembles Kalita, an aspect of Halétha which we know to be a daughter.
All three Goddesses have worshippers in Laurelorn we could in theory interact with, but for the most part it seems like there isn't much of a practical opportunity to do so. Isha is the highest Goddess of the Eonir, and the Queen probably counts as a follower of Isha, but an issue there is that the Queen seemingly already trusts Mathilde and any show of trust and faith from her could be justified on the grounds of Mathilde proving herself to her over the course of the Waystone project. A better candidate for testing this might be House Yavanna, which last time Mathilde interacted with very visibly mistrusted her, but good luck thinking of an action that involves them and isn't a waste of AP. Lileath is worshipped by House Orodreth, a pro-contact Major House we had no interaction with so far, but maybe they'll become more important to the narrative later. Ladrielle is the only one where I think we have a shot of actually testing the theory without wasting AP. House Fanpatar dominates the worship of Ladrielle, and there's already an EIC action on our docket that involves them: helping with the mist road. I guess we can do that on a turn the Father is active and check if the House Fanpatar mages on the project have suddenly stopped being so skeptical of Mathilde chisel-fingers, but the benefits if that actually works seems pretty marginal so I don't think that's something worth going out of our way to do.