Toilet Trained Havanese Peeing Inside?

We have a 4 year old Havanese. We do not show her and she was desexed at 5 months old. She was well potty trained. However, lately I have noticed she has taken to weeing either in her crate, on the toilet mat, or the bathmat! I am home with her all day and only leave her for short whiles if I have messages to do. She gets lots of attention, plus treats for being a good girl when she does 'potty' outside. She used to 'squeak' loudly at night letting us know when she wanted to go out. These days it's a very light snuffle or quiet squeak, making it difficult to wake us when we are sleeping. She has plenty of water available for her during the day. She's active, has a good appetite and appears generally in good health. However, in saying that, and thinking about it, she does tend to sleep a lot! I have MS and am unable to take her for a good walk. We do have a large, well fenced garden where she is able to run about and do her 'zoomie' thing! Really, the only problem is her accidental toilet habits. I would appreciate any help from other fur baby parents or yourself. Thank you for giving me the opportunity to air my question.