My mom is just like that. She know nothing about horses, yet she is the first in line to give me various suggestions about what should I do. My favourites:
You should stick to walking. Who needs trotting and cantering - walking is safer.
Don't do jumping, it is too dangerous.
Why are you riding without saddle? Did somebody take your saddle away?? (...while I'm enjoying a bareback ride)
Wow, he is not that smart as you're saying - look, he just spooked from that silly noise! (a loud bang right behind his back, from a car he hadn't noticed)
Good horsey, good boy! (while Snickers is trying to push her around in hope for treats, although I had instructed her that this behavior cannot be accepted)
Horses are just a hobby. You should stick to something more serious, you are an adult after all!
Meh. How I deal with it? Just smile and nod, smile and nod... Some things never change, and one of these things is a mother that is always right. But she is still a mother.