The horse seems to be very lean, maybe she is the stressy sort anyway, but that was a big over reaction on her part.
I would suggest she needs time out in the field, put on some weight and re-start from there.
Very scary, glad no serious damage done.
Looking at the going I don't think it's the horses fault it went over - it's really greasy, and looks like as it rears it slips.
Is it just me or does the horse look really long in the back and weak behind?