I'm at the part in legacy where you have to go and visit Susan in hospital. According to every walkthrough I've looked at you have to talk to the guard, pick an excuse for your name not being on the list and then select Alexander Davenport. But I can't select Davenport... I just get Roseangela saying 'I can't use that, it's a man's name'. What am I supposed to do?

You have to use the notebook to connect thoughts and draw conclusions. Remember the RA in the dorm had a girl's name, so try connecting that to Alexander by clicking both in the notebook to make Rosa think of using Alex as a girl's name.