If you stop responding at all (not just pretending you can't hear/see it), it will get bored and stop. Just disregard every post that doesn't pertain to your original post. Spell it out in sidewalk chalk in huge letters in her driveway before school/before she gets home? Write it on some paper, roll the paper up, and put it in a bottle with some sand? So it's a message in a bottle. Decorate their car?
I ran room to room by the end of the day she had 8 roses together that said homecoming and u ask her and give her a cake when u see her that's what I did in high school
Rent a horse and ride into school, take her up on the horse then ride away with her. Whoosh!! Instant prom date (Eli not Marcus)
Spell it out with paper cups on a fence. Put, "(her name), homecoming? -your name" Like, the cone looking cups and put them in the holes. Spray paint "yes or no" on the ground below it and leave the can of paint for her to answer. I pulled that one on my ex my sophomore year. I did it before her softball game so she could see it from the dugout.