it's a weird scene, but also a really good way of getting the creator's intentions across.
nina doesn't just have admiration for euphie or a girlcrush on her, but instead a deeper infatuation. i assume you haven't seen much past episode 12, but it makes her actions surrounding euphemia later on a lot more understandable with this context.
the creator could have done something else, but given that they're both women it can be a LOT harder to get the general audience to understand that there's an element of sexual attraction rather than just strong admiration. this scene, even if unexpected and kinda gross, does get the point across that she has that deeper obsession very well.
and just to add on to my comment about same-sex attraction being shown in case it's misunderstood by anyone:
even as a gay woman i struggle to know when a woman is gay or just overly friendly in media. a woman can be making non-stop sexual comments, kissing other women, and being the gayest being possible... yet somehow the creators make them inexplicably straight. it's gotten to the point i see a gay-acting woman and just assume they're straight now.
and even when they are actually gay, creators often make it more subtle since they don't want to boast stereotypes and create unrealistic scenarios, meaning that unless the couple ends up together many people just don't understand what's going on. i've watched lots of shows and movies with two characters who are (to me) very obviously gay, yet because they never officially date my straight friends just don't see any attraction between them at all.
this single scene clears up both of those instantly. could there be better ways of doing it? maybe, i don't know. i've never written a script or directed anything. but i think it does just get the point across well.