Good for your Mom!! That is really great.
All I can say is that she may want to sink down her heels a bit more, especially over the jump. That will prevent her leg from slipping backwards the little bit it did. :)
Also, I'd say allow a little more of a release. Not a lot more, since its still a small jump, but just a little more so that she is not pulling on the horses mouth. Great position for the small jump though! Its so much better to see this than see riders laying on their horses necks over small jumps.
I can't say it enough... good for her!! I would be very proud if that was my mom. :)
...he's so kissable, huggable, loveable, unbelievable...