Original tenant called very upset and is threatening to sue not only me, but the tenant she rented to.

However...I recently found out that the rent rates have gone way up in my neighborhood, and that I'm finally able to refinance since I repaired my credit.I did the math and after HOA dues of $120 (and threatening to be bumped up to $145-$160 soon), and the rate dropped from 6.5% to 3.65% I'd make a monthly rental income of anywhere from $130-$170. 

Now the mother wants all her money back, rental money included and is threatening to sue via her attorney.  

http://www.ca6.uscourts.gov/opinions.pdf/15a0662n-06.pdf@Logan Hicks this is a recently decided case where a landlord sent a letter to the debtor's attorney threatening criminal prosecution and was hit with a punitive judgment of $7500 because of his attitude. 

She threatened to file a lis pendens.

Since they were threatening.  

When my daughter fired them, and threatened to sue so they forfeited the clause in the lease saying she had to pay them the fee you're talking about - they offered my daughter's tenant another property that they managed.So, they were expecting to collect full management from my daughter for firing them, then put my daughter's tenant into another property, where they probably got paid to evict the last tenant that they themselves put into place.And the tenant they found for my daughter were problem tenants, and they knew it, and they were ready to put them into another owner's rental, where they planned to let this complaining tenant continue to make them money on all of the maintenance calls this tenant was likely to drum up.So, my answer to your question - sure it's standard. 

You are definitely in a bad position if you no longer own the property and now the new owner has a deadbeat tenant in there.Sounds like the PM dropped the ball and I would threaten licensing action on them if it were me.

We had one tenant who "felt threatened" by a tenant in another unit, they tried to use that to get out of the lease without being responsible for the rent until I could get it rerented.  

If they aren't on board you can then threaten with eviction and explain how thats a bad mark for any other future rentals.