My girlfriends mom was like your dad.
She only lived a mile from us and we tried to keep an eye on her.
Like you said, she was independent. 72 years old and still mowed her lawn, shoveled her drive, planted a garden, etc.
Her mind started to slip, yet she would refuse any help, any form of assistance.
We had a nurse/aid worker go stay with her. She (the mother) slapped and kicked the nurse and made it clear the same was in store for any others.
One son tricked her (said he was taking her shopping, the dumb ass) into going to his house to live (we didn't know his plans). He refused to take her home. She refused food, drink and medication. Four days later, she won and was back home.
Anyways, 10 days before Christmas in 2000, we had a bad blizzard. I worked nights and got home at 8:00 am. My girlfriend had to be to work at 10:00, so she said she would go to her moms that morning.
Her mom must have let the dog out before going to bed, and got locked out.
She was not the kind to go to a neighbors for help, and wouldn't break a window to get in. Or maybe her brain didn't comprehend the options. Who knows.
My girlfriend found her body, wedged between the screen door and house, probabley trying to keep warm. The dog was barely alive, curled up on her chest.
My girlfriend (we have been together 27 years) ended up in counseling, started drinking heavy (we quit 16 months ago) and is still not the same.
Still has some nightmares, still blames herself.
I don't know what point I was trying to make.
Just, don't blame yourself.
Not to be callous, but shit happens.
That is so tragic. I'm so sorry that happened to your girlfriend. I have a feeling my mum's going to be stubborn when she reaches old age, too.