from a girl's perspective, i think maybe she just wants attention from you. not in like an arrogant way, but sometimes with me, if i know a guy likes me then i'll try and get his attention and keep the "friendliness" going because it makes me feel good- even if i don't really like him back that much. that or she might feel bad for rejecting you, and she wants to be friends. since you said you only talked to her for 3 weeks, she may just regret saying no and is tryna pull you in bit by bit, or she feels bad and she wants to keep you as a friend and not TOTALLY stop talking to you. which might explain her behaviour. but since she didn't really do that before i'm a bit confused ngl with what her issue is 💀. so, maybe ask her straight up. what you did with leaving her alone i think was a sensible option to be honest, but maybe just ask her something like, "i don't want to sound accusing or anything, but is there a reason why you've been acting a little more close to me lately?" and maybe ask if it has anything to do with you asking her out and her saying no. i think that's probably the best course of action. i hope that helped- but if i said anything unhelpful i'm honestly sorry 😭