IMessage problems with user?

I'm borrowing my mums iPhone for a while and she has connected both her iPad and iPhone to iMessage and now I keep getting her message she sent from the iPad onto the iPhone. Is there a way of deleting her profile on the phone for a while, whilst still allowing her to send messaging on her iPad.

No, you are screwed forever

Settings > Messages > Send & Receive > delete her Apple ID and replace with your Apple ID.