my sister did this, she hired 2 months before giving birth. just install wifi CCTV in the house and tell the helper the CCTV is not to monitor her but for the safety of baby (and also so you can see baby when you miss baby while you are at office). this will help the helper feel less stress about the CCTV. my mother occasionally goes to my sister's house like surprise check on the helper. but must say it like "ah ma miss baby so come and visit". that way the helper cannot predict when to behave/misbehave...
so far so good. but this kind really is sometimes by luck whether you get a helper that is lovely or terrible.