My sister gave us her birthday presents back?

I felt really disappointed when my sister gave a bag full of her birthday presents back to my mom and said "tell Steph she can take anything she wants from here. I don't really need it." I spent a while finding creative, nice gifts for her that I could've sworn she would have loved. I thought about what she likes the whole time I was shopping for her- but as soon as she started opening her gifts, she seemed unenthusiastic. By the end, she said "that's it?" her boyfriend (now ex because of her bratty behavior) made her a necklace out of some of the heart-shaped coral she found on the beach in hawaii, and she picked it up, laughed, and said "wowwwww. didn't I give you this?" so anyways, she gave my mom her presents back, which is incredibly tacky. How can we deal with her? I felt so let down when I saw she didn't want her gifts, I just went to my room and cried, because I spent so long looking for her gifts. oh, and she complained about the $100 designer swimsuit we got her. I'm pretty sure she returned it...