Are there any abnormalities in the urinalysis? It does not sound like a UTI.
The first thing I thought of when I read your question was hormone induced urinary incontinence. This would explain why she seems more bloated in the morning.
If she is not spayed, however, you also have to consider pyometra. She would not be more swollen in the morning.
The other thing you need to rule out is a cancer in the bladder. She should have x-rays to examine the bladder, and possibly contrast x-rays to look for soft tissue tumor that does not show up on a regular x-ray.
The last possibility is damage to the bladder, but like with cancer and pyometra the swollen abdomen would not be getting smaller during the day.
I do not know what your financial situation is like of course but I definitely recommend that you have this looked at as soon as possible. If it is a tumor, it might be removed but if it is left too long it can grow until it is too large to remove. If it is a bladder injury, it should be closed as soon as possible.