great work there, girl!
the "why" part of it is that the appearance of apparent dementia can be caused by very many different issues. after all, largely all dementia looks like is memory problems and confusion which are noticeable and yet rather vague symptoms. so, yes, many many other issues cause the "appearance" of something like dementia.
and if you Mom's mind is NOT cleared by namenda and Excelen (both of which have heavy side effects, which may include impaired kidney and bladder functions, hence the UTIs) and yet IS cleared by treatment of her UTI, then maybe she didn't ever need them. why not ask her doctor whether an experimental drop-down in the use of those heavy meds might work for your mom.
there's nothing fixed in the treatment of dementia. it's all trial and error, you know. therefore, your own observations about your Mom's functioning and wellness and improvement or worsening are absolutely vital. speak up, ask questions.
the main thing standing between the average elder and death by medication is us, we caregivers. and caregivers who question are often the greatest life-savers of all. write down clearly what you've noticed and the timetable. this is very helpful to the doctor in making the best decisions for your Mom.
terrific that you noticed! now take it a step further. i've spent the last five years negotiating with the doctors of five people i care for. first, you notice (as you did). then you ask questions based on what you've just figured out. then, if you really feel your Mom may in fact be getting the wrong meds for her health and welfare, ask her doctor if a possible change might help even more.
doctors don't mind this. in fact, good doctors welcome it. and it sounds like your Mom has a very good doctor. and a very smart daughter who's asking herself the right questions. so now ask the doctor those same questions, but write down everything you've observed so you have the clinical data she needs to know.
don't be shy. what you see IS what you see. if there's a simple logic at work there in what you see, a doctor can see that too. you are the co-partner in care with your Mom's doctor because you see and remember (two things your Mom doesn't)
good luck and congratulations! your Mom is lucky to have you.
the UTI thing in elders is a manifestation of a) general immune system strength; b)the amount of fluids an elder is drinking (too few, for sure) and c) wiping from back to front instead front to back (if you know what i mean, ladies -- and i think you do...) which virtually all old ladies, as far as i can tell, no matter how many times you suggest they change it.