SMS Problem

You guys are way over my head! My Galaxy Ace running Android 2.3.6 is my first smart phone. When I receive texts from my daughter her number comes up one digit wrong making it impossible to simply 'reply'. If I move the SIM to another handset the problem does not follow. I assume that at some point I mis-entered her number in my phone and now find it impossible to get rid of. Incoming speech calls are no problem. I have tried clearing all the cache I could find, deleting her from contacts, removing her from History and deleting all threads carrying her number. No joy. Any ideas? I would really like to avoid wiping the handset. Very many thanks.