If I were to take a wild guess (which I did), I’d say she was from Pink Sweets; the game I’m not entirely familiar with. However, after further searching, I was not able to come across any character from that series who resembles this cosplayer at all.
I’m just hoping my readers’ guesses turn out to be much better than mine. Thanks to Ikehara for suggesting this!
EDIT: Thanks to Anon for letting me know this is Megurine Luka from the PV "Cinnamon Roll"!