I know she's not trying to be nasty, she just doesn't understand animal husbandry I guess...I think she doesn't realise that's there a responsibility involved.
The way animals are thought of the past 25 years or so is just different than it used to be. At least here in America. Probably there too.
When I was a kid vet care for small animals was not very common at all unless it was dogs and cats. Kids went out and caught creepy crawlies all the time or had a pet hamster or bunny for a while and many died early deaths and nobody shed a tear- except very young kids who hadn't been desensitized yet.
I think media has changed a lot of our attitudes about this. Also a great distance has been placed between agricultural society and the rest of us that wasn't there before.
Life and death is just a fact on a farm, moreso in yesteryear. Eating often meant going out and killing a chicken or something to eat. And even city dwellers understood a lot of that. Rodents similar your hamster competed with us for food and spread disease, so when one was seen it was killed, snakes were sometimes poisonous so they were considered threatening and icky and they were also killed.
Now there is a huge gap and we live in a kind of artificial environment that keeps us kind of innocent in some ways and allows us to be a little kinder and gentler toward our fellow beings. And in most ways, that's a good thing. But that probably isn't how your mom was programmed to think when she was developing her life view.
I wouldn't think poorly of your mum, just realize that she grew up in a different time when life was a little more harsh in some ways...
What was difficult for me was moving to my current rural community about 11 years ago and after learning I was interested in herps, everyone wanted to share stories with me about our common interest. Only their stories focused on how they run over box turtles and kill snakes. It can be challenging to see them as decent human beings, but people are complicated and these same folks often would literally give someone the shirt of their back if it would help them...