Louise making a move on Ian is weird, especially since there are very few requirements.
For now, we don't know why exactly she did it. There are tons of plausible reasons. However, I'm not sure if there is a plausible reason why she would flirt with him in every playthrough.
There is no indication she would target her friend boyfriends. She seems to prioritize devotion and romantic partners who stay together as soulmates yadayada. Jeremy not taking her and the relationship serious is already a no go for her. She expects Lena fo be faithfull for her. Flirting with multiple people is deemed as slutty, personified in Ivy, everything Louise loathes. She is against sleeping with Ian out of commitment to Jeremy and has to be pushed to do it.
If Lena is Ians girlfriend, very happy with him and not on the slut path displaying hypocritical/sexual aggressive behaviour to Louise, and also on Louises good terms (best done by bullying Stan), then Louise shouldn't have a reason to contact Ian and sent him a selfie.
My second issue is that Ian always react the same, no matter his personality and no matter if he is commited to anyone. His behaviour is very smug, condescending, aggressive and fits his chad path, but for regular, sensitive Ian focused on relationships and not just sex, its out of character. A variation in which he is much more hesitant and reluctant should be mandantory. Imagine early Ian texting with Cindy that agressively, its inconcievable, considering how delicate and careful he was there, overthinking every step and reading every signal. Being unable to flirt with Louise or doing it and emphasizing that he cheats on his partner (and not half heartely at the end) should be included, as well.