Looking for my backbone..

Hi guys, looking for some advice.

So in the last i’d say 8 years or so (since having kids), i’ve noticed that i’ve become much more inside my own shell. I used to call people out on their bs and was not afraid of confrontation, but now someone could literally slap me in the face and I’d say sorry. I’m struggling right now as I have this ‘friend’ who makes so many comments about me and my kids and I always think of things I SHOULD have said, but just ignored in the moment. This heffer needs putting in her place lol.

How should I go about becoming less of a door mat to people?!