Tonari no Onee-san ga Suki - Vol. 3 Ch. 25 - A somewhat dissatisfied Shia-san

[Bonzalez]

On the contrary, this chap gave MORE hints that she is indeed beginning to see him romantically, and is trying her best to avoid thinking about it.

There was a lot of subtext hinting to her being jealous he would go with another girl to see movies.

And her insistance on her not wanting them to see FLCL cause of the "older girl x younger boy lewd scenes" screams of her projecting her own thoughts of her relation with the protag.

I agree with you, but wanted to point out her jealousy wasn't subtext. It was text when she said "That was my line," meaning she felt the same way he did about her movie buddy watching movies with someone else