From a chick, for what it's worth - don't you DARE take it back!!
She will be more mad if you take it back than she ever would be over the money spent.
She obviously loves you and wants you to be happy. She wouldn't have encouraged you to buy it unless she wanted you to have it.
She seems an extremely cool chick. Some chicks would say "Buy it" and then be pissed when you did.
She's not one of them.
Wear the jersey with pride and to victory!!