Can TIA cause personality change? Dementia?

My mom has commonly not accepted ownership for the problems she has caused herself, but has always kept her mouth shut with strangers. This is not something new. She has experienced multiple mini strokes (TIA's) over the past 2 years. At times it is nearly impossible to understand her because her speech is so slurred (sounds like she is talking with a sock in her mouth). She refuses to go to the hospital. We have called the ambulance and she turns them away. She has heart/kidney failure, ulcers on her feet, and horrific control of her blood sugar. She is 67. Lately, she has seemed to be overly agitated, yelling at doctors, and snapping at people when things don't go smoothly. For instance, she chose to switch her Medicare for an HMO and now realizes that the coverage is crappy. I had told her before, that since I worked at a health insurance company that sold Medicare riders and processed claims, that I would be more than willing to look at the different types of insurance for/with her and explain in plain english what each plan covered and didn't cover. I have offered every year. She neglected to take me up on my offer and blames my dad for her signing her own name for HMO coverage. No one forced her to sign her name. I offered to help, and she refused. I don't feel bad about her picking crappy insurance. She made her own choice, and refused help, so that's on her. The insurance only covers a certain brand of Rx and she wants a different brand (due to side effects). I told her that some medications have lots of side effects, and she might just have to make a choice between treatment with a med and non-treatment. Instead of telling the doctor she was willing to pay cash for the certain brand name script she wanted (She definitely has the money to pay for it), she doesn't even ask for the script, forgetting that she could pay cash for it. I had to remind her that she could always pay cash for an item if the insurance didn't cover it. She didn't seem to remember that was even a possibility. She got angry at the doctor and started to tell him off. She yelled at the woman in the pharmacy over a little misunderstanding. She is not pleasant to be around. Is this something that a TIA or mini stroke can cause? Could this be a sign of dementia??