My girlfriend is ignoring me?

This is on behalf of a friend of mine. He and his girlfriend have been in a long distance relationship for a little less than a month now. They live almost 8000 miles away from each other. He's in the UK while she's in the US. Well lately, she has been ignoring him a bit frequently. She'll text him, and then not answer back for a long while. Her excuse always seems to be that she "didn't receive the notification". He has created an anonymous profile, and when he texted his gf using that account, she almost immediately responded and they talked for hours. She went on about how she feels like a terrible girlfriend and how she doesn't believe that he really loves her. He wants to talk to her about it all, but is scared she'll get upset and he doesn't want that. What should he do? Thank you. :)