I have relatives who are vocal about their insecurities and seem constantly mortified by how others might perceive them and their actions. We don't see them that often, but when they've done this in front of my children I tackle it by countering their logic to de-normalise it. For example...
Them (nearly tripping on uneven ground, whilst going bright red, looking around them in a flap and generally drawing attention to themselves): eek, how embarrassing! Oh, cringe. Oh, how embarrassing!
Me: is it actually that embarrassing? Everyone nearly trips now and then, you see it all the time. Most people just carry on as if nothing has happened. It's not a big deal at all.
They do it all the time, taking about not doing something perfectly normal, such as getting a refund in a shop, as it would be cringe worthy, or being vocally vicariously embarrassed if I ask for a table to be wiped in a cafe, etc. Simple statements such as "people get refunds all the time, that's why there's a returns counter" put it into context.
As my children have grown older they see how limiting and dysfunctional it is to be so overly aware of how you might be perceived, and this has helped them to be assertive so they don't limit themselves in the same way as these relatives. They've expressed how sad they feel for the relatives but realise it's very much a them issue.
We have a family friend who's always going on about her weight, and I tackled that by chatting to my children afterwards about how some people have unhealthy attitudes to food and their bodies, and how this can occur, including by hearing other people talk about it and thinking that's how everyone thinks. This has worked well.
So even if your mum does say things it's not necessarily going to normalise it. Children will hear all sorts of terrible messages, but if you encourage them to question people's thought processes and not take them at face value it's a skill they can apply over and over again.