What To Do If You Think A Female Friend Is Annoyed At You? (all Answers Welcome, Female Answers Better)(long)?

firstly let me just get one thing straight, friend means friend, she has a boyfriend already, and so we are just friends. however, i do like her, so I guess your thinking, does she know? Well, the answer to that isn’t immediately clear, my friends have mentioned it to her somewhat indirectly, they thought it would be funny to write it on one of the walls in our 6th form last year (i was very mad btw). so, after this she was very upset, thinking that people may start rumours, following this I got a bad email of her boyfriend (not threatening though) I was quick to respond bye lying, saying “no” I didn’t like her and its just someone playing a prank, and although they both seemed happy with this, she never really seemed, quite as freely comfortable with me again as she did before.
(it may be worth mentioning at this point that i have no problem with her boyfriend, although I don’t know him really well, he seems a great guy)
so, year 12 continued with her continuing to be ever so slightly less comfortable with me, but not too much. I put it down to something that was natural considering what had happened and decided to just let time heal it. then end of the year came, and so yr 13 stared, for the first few days things where great, I didn’t talk to her as much as I might have wanted partially due to the fact that she seemed busy with her other fiends or her boyfriend, and partly because I feel that due to the fact I do like her, if i spend to much time it might become apparent.
so now a week or two has gone bye, and it seems as though she no longer wants to talk to me, i mean she will if i come up and find a reason to talk to her, and she doesn’t seem, cold in anyway but it would seem that every time i do, she has something to do or somewhere to go, a few minutes later. she youst to come up to me and talk to me herself sometimes but now that never happens, if we talk, its always because im the one going to her.
another example would be that she would often sit next to me when she came out of lesson, now you guessed it, she doesn’t, it seems she is even avoiding me, seeming to sit with whichever group that i happen to not be with at any moment.
so what do you think? i know that she is defiantly less friendly with me than she was but i have no idea why, maby its subconscious, and its simply due to the fact that i didn’t talk to her so much at the very start of the year, or does this sound like the symptoms of when a girl is annoyed at me, or perhaps the thing where she heard rumours that i like her have come back to haunt me, perhaps she decided that there was some truth to the rumours she herd and decided its best not to be as friendly with me or perhaps her boyfriend surjested it
as you can see i really have no idea so i hope you can help
Background knowledge:
we where originally friends in primary school, then didn’t see each during secondary school and then met again at the start of 6thform
my feeder secondary school was boys only so i don’t have a lot of experience with girls
she met her boyfriend in our 6th form when she joined last year
in the early days of last year, she youst to be quite flirty physical with me often touching me and standing very close and multiple people thought she liked me, but i never encouraged her, partially because she had just about started to go out with her boyfriend and partially because, as previously stated i wasn’t very comfortable around girls at the time despite the fact i was 16, however it must be remebered that that was only for around 1/2 to 3/4 of a year ish in year 12
right so onto the actual questions:
1: why do you think she isn’t talking to me
2: do you think i should confront her about it (in a considerate no-accusing way)
3: are there any other reasons that you can think of as to her behaviour