We are pretty sure Mom is in last stages of MS. She keeps thinking she will get better. She is showing many signs.

Please don't burst her bubble of hope. It may be all she has right now, and she will need to hang on to that as long as she can.
Your mother is well aware of the progression of MS according to what doctors say, but maintaining a positive attitude is paramount in conquering any disease or illness, so just let her be.

And just to share a true story about a young man(early 40's)at my church who has MS, and was wheelchair bound for several years. He had to give up his career in the medical profession because of his MS.
One Sunday he decided to attend a local "spirit-filled" church, and went up for healing. Within weeks he was up out of his wheelchair and walking again with no assistance, and over time he was able to return to the job he loved and had previously lost. He shared with me over the weekend that he now takes none of the medications that he used to, for his MS, and that his doctors are in awe of his improvement. We call it a miracle and say thank you Jesus!!!
So the moral of the story is to never underestimate the power of Gods healing and ones mind.

I think you need to step back and rethink your plan.
Quitting your job to take care of mom might not be the best plan.
You will lose income. Unless mom pays you. And if this is the plan then set it up properly so that taxes are taken out. Draw up a Caregiver Contract. I suggest that you make it for a span of 6 month and then review it.
In 6 months everything may be the same
OR in 6 months you will be doing more than you expect and find you can not handle it
OR mom will drive you absolutely bonkers and you will be looking for an escape plan.
If mom is a Veteran check with your local Veterans Assistance Commission and see if she qualifies for any benefits.

Just know this...
Mom WILL fall it is not a matter of if but when. The fall may be minor or traumatic. Will you be able to care for her if that happens?

YOU can not "make" her understand what is going to happen. This is something that she has to accept but accept or not she will decline.
If you intend on caring for her you need to be aware of the symptoms and the effects.
One other note of caution. IF you are the one that is going to give up a job, if you have siblings that think she is safer in a facility that can care for her 24/7/365 please do not expect them to share in the caregiving.
And if you have a family of your own do consult them before you make this decision.
Sorry if this is sounding like I have tossed all your plans out the window but you have to enter caregiving with Eyes Wide Open.

I had a great Aunt that had MS. All of her doctors told her she would be wheelchair bound within 10 years from diagnosis. 40 years later she would say, "I didn't buy into it then and I am not buying into it now." At 80 years old she used a walker when leaving the house and finally had a ramp put on her snow bird house.

She was a retired RN and she believed that you didn't succumb to what a doctor thought he knew. You kept active and pushed yourself and believed that you were okay.

She lived to be 90 years old, never wheelchair bound and she died of complications of Alzheimer.

There is something to mind over matter. Not just if you don't mind, it don't matter, either.

I agree….it is a coping mechanism. If it won’t hurt her then why make her understand. I know it is hard, we have been trying to do it with my mother. We explain and explain away but it is her coping strategy(denial). We now just go along with her. Although mom does not have memory issues, she is medically complex that leaves her in daily pain. For example driving…..until she was out of denial for driving it was always explaining until one day we just let her know that if she wants to drive then go ahead however grandchildren not allowed in vehicle with her. It took months for her to come out of denial and now accepts that she can not drive any longer(pain, pain meds, slow reflexes from pain med and inability to lift leg due to pain). That is just one example but it was then we realized she needs to come to terms on her own through the denial process.

She may need her denial to just cope. Leave her be, who is it hurting really?