Text troubles.

I had been talking to a friend and the conversation ended with me agreeing to look up some details and text them to her, which I subsequently did a couple of hours later. Next day she calls and asks if I sent them as she hadn't received a text. I said I had and sent them again. In both cases the delivery report came in as saying 'delivered'. Half an hour later I get a text from her saying she still hasn't got them. After a few more calls and some test texts it looks as though she is not receiving texts from me, however I'm receiving texts from her without problem. She said she'd get her son to look at her phone (she's not all that tech savvy and basically just uses her phone for talks and texts), came back and said he couldn't see anything obviously wrong. I have not had any indications of problems with texts not being received from other friends. I'm on Virgin and she's on EE. Anyone aware of any problems sending/receiving texts between Virgin and EE?