Just tell her you are moving out of state. Is she so crazy thats going to send her over the edge? Not like shes going to travel to you? Its possible, of course, but IME, its when you switch to a competing trainer in the local area toxic trainers really go off the rails.
If you are really concerned, arrange to ship the horse out the end of July, give notice and a check for August as you load up. Thank her fir all shes done for you, wish her well. Then GTHO.
Depending on your barn, you might want to not share your plans with fellow boarders, they’ll tell trainer and she could get ( justifiably IMO) upset you told everybody but her. Don’t do that. Sometimes when everybody in a sketchy, unsettled barn environment knows you are leaving, your stuff starts walking iff, they figure you wont miss it until after you are gone. Not talking about the trainer here, your dear fellow boarders.
This topic comes up on here often. Most of the time the shock is there no trouble and posters learn they were never friends, just a very small blip on trainers radar and not as important as they thought. Maybe financially important but personally, trainer couldn’t care less.
Don’t be afraid to act, its a positive change in your career and life. Keep you mouth shut, round up your stuff, slowly start taking it home for “cleaning” or repair and start arranging transport. Commercial haulers don’t have enough drivers, book well in advance.
And remember, its your life and your horse. You don’t owe her anything other then 30 days and polite thanks. Stop letting her control your emotions and enjoyment of your horse not to mention ruin your move.
And NEVER board/train anywhere with anybody without a signed CONTRACT again. That just enables sketchy barns and bad trainers to stay in business.