Is my boyfriends sister ungrateful or no? Should I get her something for her graduation or no?

lexih_919
So I have gotten her a sweet 16 birthday gift that I gave to her in person and she didn’t even say thank you to me. I had to message her to even get a thank you out of it. Also I got her a Christmas gift and she ruined the moment and made a rude joke that upset me. I said happy birthday to her and she didn’t say thank you. Her high school graduation is in June. I’m starting to not like her. Her family wants me to go but I don't know if I should. I don’t think I should get her a gift because she’s ungrateful. I feel obligated to get her a gift because of her family or I feel they will look down on me. But I’m tired of the way she treats me what should I do?
Is my boyfriends sister ungrateful or no? Should I get her something for her graduation or no?
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