I don't think that the trim alone would cause lameness. It's not horrendous, just not great.
Due to lack of toe callous she could be more sensitive; if there is a great deal of thrush there that has progressed, that could make her sore. She could, as suggested, have some soft tissue strain that could make her off. This would be due to the long toes, or being out of balance, though I can't see that on these pics. Not saying it isn't so, I just don't see it. Or it could be a combination of factors, one of which could be something totally different - like she smacked her foot on something without you realizing. Also we are seeing only one hoof here. If I had to attribute lameness to the hoof, I would go with thrush, but that's a stretch I think.
As for the mustang roll -- If your previous trimmer said she was doing a mustang roll, that's probably all she was doing. She may have been a bit more aggressive on it to relieve the crack, but maybe not. W/out pics of course we can't even guess.
Personally, I'd put up with the nutty trimmer if she treats my horse right rather than the polite farrier who screws it up. Who are you gonna call this time?