Her sway back will make her hind end weak. You can get saddle pads that are built up around the withers and make sure she has enough pads so the saddle fits comfy. Even bareback it may help distribute the weight more evenly.
Her Knees look a bit puffy, and in one photo it looked like she had to long of toes in front. Or not enough heel. Something is off on her front feet. She is cute. Just be kind and don't ask a lot of speed or steep hills and she should be fine.
Lordosis is almost always, 100% genetic. Because of this, I don't think this mare should be bred. It is well known in Saddlebreds and a few other breeds. It could be bred out of horses entirely, if nobody would breed such horses.
That said, most with much worse cases than this mare, can be useful riding horses, well into old age.
She's a pretty girl. Just a bit straight in the rear I think and maybe a little clubby in the right rear. I think she should make a nice riding horse for you, for years to come.
Most do ride these horse with saddles, since it distributes the weight more evenly over the back.