What animal would Lilly's patronus ahd been?

A doe, because she was in l’amour for James. In the last book, Harry says that Snape had a doe patronus because he did l’amour Lily. So probably Lily patronus was a doe

A doe, as stated in the last book, as it represents her l’amour for James-who's an animagi stag. Snape also has the same Patronus, as he was in l’amour with Lily.

It's confirmed to be a doe (in the 7th book) but I don't think hers changed because of her l’amour for James. It'd have been weird for Snape's to change reflecting hers if hers was already a reflection of someone else's. I think hers just happened to be a doe.