I'm so sorry for what your mother is going through.
Several years ago, one of my cats fell behind our computer desk and was caught in the cords. In order to free her, I had to hold her down, definitely against her will, to unwrap the cords from around her leg. She was not happy with me and proceeded to bite my arm several times. We called a friend who is a vet tech and she told us to not mess around with cat bites. The bites are very deep and heel over very quickly like a puncture wound. Cats mouth's are very dirty and all of the bacteria gets trapped in the wound making it very suseptible to infection. I was put on heavy dose antibiotics and had to get a tetnus shot. The next couple of days, my wounds on my arm felt like they were on fire to the touch. I remember my DH saying "there is a war going on under your skin!" Luckily, since it was my cat, I knew rabies wasn't an issue.
After my "incident", several people I knew told me about similar stories of cat bites they or another family member had received and because they didn't go to the hospital right away they ended up with horrible infections. I hope that they are able to find the stray so your mom doesn't have to go through a rabies series.