Hello, I am a solicitor with over 15 years experience. I will try to answer this question.
Why can't the Landlord have acces to do the work without your daughter being there?
I think she should let him in when she is not there to carry out the works otherwise she may well be part liable for any damage caused by the damp. There is no good reason that you have shown for not letting him in at normal times when workmen normally work.