My dog also assumes all strangers are friends, and all dogs are enemies!

They didn't do blood work, or even x-rays because her x-rays from 4 years ago were so bad they told me back then that euthenasia wouldn't be unreasonable, and that x-rays now would certainly be at least as bad and there is nothing new to learn from doing them. But she still has mostly good days.  Sure, it is hard for her to squat and poop, but she does it (mostly on one leg now) and she poop-walks before it has all come out.  She can't run, but she walks down the street and back with me... usually very slowly on the way back.  And she eagerly comes out to the sheep when I move the sheep ... she is most alive and happy out near the sheep.  She wants to ride in the truck everywhere I go, and I always bring her so she can enjoy the sights and smells without having to walk.  I have a ramp and I back up to the deck so she walks only a slight incline to get in and out of the truck.  But most of the time she just holds the floor down, sleeping near me in my home office.

If she can't toilet herself, that will be enough for me to take her in. 

 I'm really glad you gave her the 4 years without a doubt, she sounds like a very happy girl, I'm sure she wears a big goofy smile proudly with you around. You are her safe zone, and for as long as she has to live, she knows that she can be happy and safe with you around and that's everything ❤️