Hey there! Typically when issues aren't being received, it's on their end, not the senders.
Is she using the native text app?
Good morning, magenta811193!
I see you're new to the Support Community -- welcome! I agree with Lauren that this is likely not an issue with your phone or service, but rather your friends. Does she have T-Mobile as well or does she have the same issue with receiving texts from others? What type of phone are you using and what type of phone does your friend have? We'll do our best to get you answers.