Personally I would have left after that first incident. She should have taken you down to a lower skill level, and worked up from there again. Not insulted you.
How old is this girl? Sounds like politics might be involved in her "business decisions." (I.e., sounds like she could be a drama queen, and kicks out whomever she doesn't like.) There's nothing you can change about that, unfortunately. If her parents are letting her run the show, and you're worried about her kicking you out, then all you can do is move.
The incident with the clippers shows me that she has no idea what she's doing. You introduce clippers slowly. Just the sound at first, for a few minutes, a few feet away from the horse. Eventually you get to where you can lay the BACK of the clippers on the horse, and they will get used to the vibration. Once they get used to the vibration and sound on various parts of their body, they usually won't get anxious. If they do, you need to back up a step and try to get them desensitized again. You can't rush it. Horses are prey animals. For all they know, that tiny little buzzing thing may kill them!
Your friend's mother should have demanded a portion of her money back, and/or stated that she would be going to a different trainer. Sounds like this girl is getting a little big for her britches. If you pay for an hour long lesson, you need to get an hour long lesson. There's no excuse for ending it sooner, unless the rider gets hurt, or the horse goes lame. I've had both happen to myself, with different trainers, and it's always been no charge for the lesson. If one of my trainer's goes over with the previous lesson, then my lesson still goes on for an hour, regardless of how long or short the previous lesson was. You should never be penalized for someone else's longer lesson! That's ridiculous!
Are you worried about this trainer coming after you, or just seeing if this is the norm in the horse world? Bad people are, unfortunately, everywhere.