How do I prevent my VA from stealing my IG account (changing the password and email) + sabotaging the account?
The VA’s jobs are:
post stories (on the spot) along with editing them with location filters, etc
DM other accounts that aren’t following me
Is there a software that lets them do the above? Also - How do I protect myself from the VA stealing my password/login and locking my out of my account?
There is no such way to do this to my knowledge.
If the VA is from the same country as you, put a contract in place. If they’re offshore, then it’s down to plain trust.
Get something like Multiloginapp or Dolphin Anty login with that acc on the browser and add the VA as a teammate for the program so he can login on the app no password needed since you already logged in on the browswer for him. it’s gonna cost you a $ but thats the choice you have to make 
You can use Dashlane to encrypt your password. And setup all 2FA features before. That way if it comes to an account loss, you can get it back with previous personal informations you’ve used.