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is this an assured shorthold tenancy agreement ?
Either way, she is under a duty to allow reasonable access which would include marketing.
You have to give notice by a received means of no less than 48 hours and the offers of viewings do have to be reasonable. However, she cannot just refuse all access.
if she did you could, in principle, arrange a viewing without her consent although you would have to jump through a lot of hoops.
I suppose you could try to sue for the vacant month but the normal and time honoured method of enforcing this is to offer no less than three appointments by a received means with proper notice periods. Then if they are all refused pursue a viewing during reasonable hours.
Can I clarify anything for you?