This is one reason why I never, ever, ever give a forwarding address to old neighbours! (Or a phone number.) Although I get that you would not have changed your mobile number when you moved, and if she was a friend, she would probably have it.
Reminds me of many moons ago, we sold a house to a couple, and when we saw them a month later, (in the shopping centre,) they moaned that the boiler popped and banged when the heating was on (lime in the system!) and the 12 ft high fir trees needed cutting or they couldn't get full insurance cover. So they wanted US to pay for British Gas to do a system flush, and also to pay for someone to cut the fir trees down by 6 feet. 'YOUR BOILER is noisy' they whinged. errrrrrrr, no, it's YOUR boiler actually!'
We explained to them that it wasn't our house now and wasn't our responsibility.
When we saw our solicitor a few weeks later, she told us that this couple had been asking for the address of the place we had moved to as they wanted to come and see us! THEN they told her why! She explained firmly that not only was she not going to release our new address, but also, none of what they were complaining about was our responsibility.
OP, it may be a good idea to contact your solicitor and explain what's going on, as she may be able to send the batty mare a (warning) letter, and you can get your side in before SHE does IYSWIM. And I agree with others that you should keep all her texts. Don't delete them.
And I definitely don't think this friendship can be saved. If I was the OP, I would never want to see this bloody woman again!
And I also read it that the OP had already sold the house. Although she should probably have put 'NOW we have completed legally,' not 'ONCE we have completed legally,' as it implied a tiny bit that she had yet to complete. So it was understandable that people would have got confused.