Everyone has already given really good advice. I agree with it.
It would be better if you just leave her alone for the time being...she does have someone she is already in a relationship with. You, of course can still be friendly to her and be friends but its good advice to not push yourself too much on her especially when she is trying to be faithful to her BF. It will only make her not like you and push her away.
IF she was you GF how would you feel if another guy were texting all the time and trying to get next to her and kinda distract her from you? I am sure you wouldnt think it was fair. She is already with someone else, it just happened that way so you need to accept it for now.
I think its wise to just let the relationship she has with her current BF just play out. If you remain cool and just continue to be kind to her but not pushy who knows what might happen between you. She might even take more notice.
I know you really like her but for now just be patient and wish the best for her. You may be surprised and even find someone else just as special as she is when you least expect it.