My sister doesn't like my boyfriend. What should I do?

Anonymous
So we're with my boyfriend already 7 months together and she still doesn't like him. Whenever I ask her if my boyfriend could come even for a short time but she says no. And if I ask her why. She only says that she doesn't like him. Sometimes I invite him over and don't care about her opinion. Sometimes they talk like friends but another times she ignores him, go to another room and watch videos on her phone. My mum said she just doesn't like him because we're not doing anything with her. But that's not true. We play board games with her, try to talk to her, he often shows her what music he likes and she has the same taste. Sometimes I find them similar.

Now she's not even saying hi to him. Unless he's with dog. Dog changes everything.

Is there anything I can do?

She's 12.

I think she will grow up, have her own boyfriend and will understand. But I'm heartbroken right now. From very early days we were always together, making fun of our cousin together, everything we did together. And now sometimes she even doesn't want to talk to me. Help?
My sister doesn't like my boyfriend. What should I do?
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