Do nothing.
this is the tough bit. do not answer, do not rise to it - she has sent this as a Call to Action, and this is a trap.
You were expecting her to nudge you, threatening to come around is her nudge that she doesn't want to be ignored. it's either her hoovering, she'll come around and be all nicey-nicey and never mention her email again, knowing you will be too frightened to do so, or her goading you further. Either way you can't win, so don't even agree to play.
If she turns up, refuse to answer the door.
If she kicks off, call the police. Seriously.
My DM moved house without giving me any details (this being the last straw, she'd left me out to dry with my abusive ex, having actively sought to keep me in that abuse but not as badly and overtly as yours) She contacted me 10 days after her move as if nothing had happened and i emailed her with my bewilderment at how she can have treated me like that. I got a ranty, well we were never THAT close/in each other's pockets/gradually drifted (yeah dropping me like a sack of shit when my world fell apart'll do that
)
I told her I needed time and space to process my hurt. She started calling me once a week on the same day, same time almost to the minute I let all the calls (weeks and weeks of them) go to voicemail. her messages were bright, breezy, as if nothing was wrong, that there were no issues and secure in the knowledge that eventually I would STFU about it.
I didn't bend. I didn't answer any of her calls. Eventually she and her vile H turned up at my door, uninvited and armed with enormous gift for DS (manipulative.... he answered the door)
They started the hoovering process again, I called them on it, saying that we had not resolved why they moved and didn't tell me where etc. Her H started shoving DS up the stairs, I told the H not to, he didn't and I told him to go, for them BOTH to go. they refused, I had to call the police. During the melee, i was told to 'Do what I was told' I pointed out that at over 40 years of age, I would NOT be 'doing what I was told'
The buggers actually sat their arses down and WAITED for the police to come and make me see sense 
Eventually they left, being told NEVER to return/contact me. I gave them ONE chance last spring, she blew that again, no mention, no apology, no recognition of their abysmal behaviour and a general bulldozing to get back into my life. I refused.
None of this stuff is easy to work through, it hurts like nothing else in the world, and I would not wish it on my worst enemy. you have to be strong, you will feel scared, you will feel like you are making a fuss over nothing, but my lovely OP, you are NOT making a fuss over nothing, this woman failed you catastrophically.