Dad has dementia, and now so does my mother might as well. She's his caregiver. What should I do?

I'll try to make this short and to the point, but the whole situation has been going on for, well my whole life, but it's gotten serious the past few years.

My dad has dementia. He was diagnosed about six years ago, and we think he probably has had it for 10 years. It's been very slow progressing, and luckily he was close to retirement and only retired a year early. My parents are fortunate enough to have money, but the fact that he may eventually need to go to a nursing home, along with my mom's bad spending habits, worries both myself and my mom. As a side note, of course I would love to be left with an inheritance, but I would rather see my parents get the care they need and go through less stress now; when my grandfather died two years ago (after requiring 24 hour care for two years prior to his death), two of the four siblings' desire to have an inheritance tore the family apart and caused major problems that still aren't resolved. So, when I mention money worries I am speaking from the perspective of wanting my mom to come to her senses so she CAN afford a nursing if need be, and not blow her money on useless crap.

So, my dad was diagnosed with dementia. He is now 69, and has some very noticeable memory and cognitive decline (sits in front of the tv all day, doesn't shower for weeks at a time, eats constantly - and he has diabetes, repeats himself/asks the same question every two minutes), but he's still aware of who people are, where he lives, major life events, etc.

The problem is my mom. I would consider what she does neglect - certainly not intentional, she loves my dad and BELIEVES she is/would do anything for him, but she just makes it worse. If I go into the way she interacts with him it would take forever, but for instance, she SCREAMs at him to take a shower, so he yells back, and never gets in the shower. The reason is that she will only think to get him washed up when he has a doctor's appointment, people coming over, etc., and so she asks him last minute. Then, her anxiety kicks in and she screams because she realizes he won't be ready in time. It drives me CRAZY. Sure, he's gotten slower. Things like showering simply take more time. But, I can get him in the shower within a half hour, no argument. And I make sure he does it the day before, and I also try to get him to shower whenever I visit - sometimes successfully, sometimes not. But, this causes my mom to rely on me. She has become so hard-headed - when I talk to her, she CLAIMS to understand where she goes wrong, but then she just turns around and does it again.

While this is simply characteristic of my mom, things have gotten worse with her in the last 2-3 years. She shows very noticeable cognitive decline, which she attributes to stress/anxiety/depression. I understand this may be true, she lives in am inherently stressful situation as a caregiver. However, she causes probably 70% of the stress in her life by the way she reacts, or by creating things she has to do, or problems that don't exist.

She has always been a shopaholic, and there is always something she NEEDS to buy, some project that needs to be done, etc. She buys in excess. I know most grandmother probably spoil their grandchildren - my daughter literally cannot fit another outfit in the closet! My mom always was messy/unorganized and bought in excess, but it really got bad 3 years ago. My parents remodeled most of the house, meaning everything had to be packed up and shuffled around. It piled up upstairs, and never was put back. Then, in my mom's typical fashion, she bought more, didn't use it (because she really didn't need it), so that piled on top of her piles of piled stuff! And it just keeps going, never getting better, only worse. She starts to clean, only giving up halfway and piling the rest of what she didn't get through in one room so that she at least has one clean room in the house (which she fills up within a week or two). The kitchen is disgusting. She has a huge kitchen and about 5 sets of dishes for the parties she used to have, so she simply doesn't do dishes until there is not a clean dish or an open space in the whole kitchen. She finally hired someone to do dishes and clean for her, which in itself helps.

I feel like, both as a daughter, and a social work/gerontology student I am neglecting my parents. But I have no idea what to do. I am a single mother, full-time student with full-time work. I can't be a live-in caregiver, and it wouldn't be fair to my daughter. And my mom refuses to get help with my dad or acknowledge that she has a problem. I constantly feel hopeless. When I am at there house, I just want to leave. I know there is nothing I can do that won't start an argument, and seeing the condition of the house and my mom's behavior, and my dad's reaction to it, and the vicious cycle that creates - all of it literally makes me sick to my stomach, makes my head spin. I go home and mope all day I get so depressed from seeing it