Sorry that this is a late reply. Does your country have any legal recourse for harassment or stalking by a relative? IF possible, such charges can put a dent into your mom's pursuing revenge or hoover tactics, as such public records show up on her record and have consequences such as heavy fines or imprisonment, if caught. Just something to consider if you wish to consider legal action. Start by keeping a record of all her phone calls, emails, visits, etc to build up a proof record when you report to the authorities about her actions. It won't totally stop your mom, but it may take the claws out of her when she realizes the legal and financial implications.
OTOH your other half has a point about ignoring her. This may mean moving to a new address, with new phone #, new everything, including new jobs about which you don't inform your mother or her monkeys, including possibly your sister, it's like dropping off the map. A rather drastic measure, as it's a last resort to cut off family. That's a nuke option that not many ppl take, but it has worked for some.