There’s lots of resentment in you, OP, and quite a lot of inferiority complex towards your colleague - as you have repeatedly written, because she’s younger, pretty and gentle. Something you can’t be.
As a teacher, you should well know that it takes a lot more that softness and prettiness for kids to respect a teacher. True, maybe they are drawn to her because they have tough home lives and not enough affection there - so softness and gentleness can go a long way. You said yourself that your ultimate threat to the girl in question is calling her parents - sounds like her parents give her hell whenever you complain to them about her.
But on the other hand, if anything, youth and softness can make a teacher an easy target for tough kids. Your colleague has probably worked very hard to get this level of respect from the kids DESPITE her youth and softness. Maybe they know they can go to her for advice and emotional support with any problem they have? Maybe she shows them mutual respect and understanding? Maybe she took the time and trouble to get to know them really well? Maybe they know she’s strict but always fair? Maybe they know what she expects of them and what the boundaries are they must never cross? It really has nothing to do with looks and accent.
Why, instead of quietly simmering, don’t you talk to her about this incident, tell her how it made you feel, but also mention that you admire her way with the kids and how she got there? You’re on the same side after all, and sharing experience and the knowledge of your pupils can only help.
So stop moping about your looks and accent, OP. If it helps, one of the best and most respected teachers in literature was just like you: tough, strict, hardened, no-nonsense, with a thick Scottish accent - Professor McGonagall. But she was also impressively knowledgeable, she was always just and fair, and took the kids’ side when necessary. No kids messed with her.
Good luck to you and your kids!