From her perspective, she is only taking what you are offering to give. She doesn't see herself as doing anything wrong.
One does have to wonder why you are offering to give so much to someone who offers so little in return. It won't mean she'll like you any better. She'll just enjoy the gifts you give her, but it's the gifts she's happy about, not you. I think you'd be better off saving the money you're spending on her gifts.
As far as spending time with her, that's your choice. It does seem to be a pretty one-sided relationship though. I can't help wondering if you are really satisfied with that, or if a part of you is just waiting for the feelings to be reciprocated. What you're seeing is what you're going to get. You're being unfair to yourself by investing in somebody who won't return the feelings.
“This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.” ― Douglas Adams, The Hitchhiker's Guide to the Galaxy