babycat,
Just a thought but have you tried sending an e-mail to the Commission for the Disabled in Malta?
You can find their e-mail address and telephone numbers HERE click on the left where it says "disabled visitors."
Sorry but the only hotels I can think of at the moment that have a walk in shower are the Intercontinental and the Fortina. The Intercontinental does have wheelchair access and reserved parking for people with walking difficulties, but I am not sure about access at the Fortina. I also read that the new Meridian at Sliema will have wheelchair access and special adapted bathrooms, but is not due to open until March. Sorry I cannot be of more help, best of luck.