Woman refuses to help sister buy Plan B; says, 'She needs to stop being afraid.'

AITA for not going into the store and buying my sister a plan b because she was too embarrassed

My sister (18f) has social anxiety, and she’s just a very awkward person overall. Yesterday, she asked me to go in the store and buy her a plan b because she was too embarrassed.

Also, they had them locked up, so you had to ask someone who works there to unlock it for you, and my sister gets anxious going up to and talking to people she doesn’t know. I told her she had to go in and get it herself.

She got mad at me and said I was being a bad sister because she asked for a simple request, and I should've done it, knowing she has social anxiety.

I get where she’s coming from, but I also feel like she needs to stop being afraid and learn to talk to people, even if she’s embarrassed. She also would’ve done it if I wasn’t there. AITA?