Am I selfish for not wanting to share my birthday money with my sister?

I am 28 single lady and my friend sent me $1k and my sister found out he gifted me cash. My sister is demanding me to give half of it once I receive it. Like she always orders things from online shop and never even buy me any. Plus I know she's struggling since she has a daughter who just started college but I also want to buy something with that money for myself. Am I selfish for not wanting to share it to her? I could just say I did not receive it or its a scam
Am I selfish for not wanting to share my birthday money with my sister?
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