The impression i got was that Eli was already quite aware she has interest in women, just perhaps a bit shy in general rather than openly hitting on everything that moves. She readily answers to Lena's flirting and at no point she made me think it's a first for her.I get the impression that Lena might be the first time she's encountered a serious attraction for another woman, she seems cautious in a way I have seen with bi-curious women before, but Eva has yet to really reveal much of anything about her yet.
(tbh, i'd prefer it this way -- can't help but see the "i never thought i was into girls" as a very tired trope, and so are the "i shall blatantly hit on everything that moves the moment i see her" characters. It'd be nice, and pretty rare, if there was someone who is neither of these and more in the middle of the spectrum)