Re: Calling all lawyerly types....
For not much money, and maybe none at all, depending on the lawyer, she should be able to find someone to talk over her options. Did the letter come from a lawyer or from the former client herself? If not, she might be blowing smoke. A lawsuit would take time and I assume she wants to sell her house now.
The statute of limitations may have run on any overcharge claim.
Any overcharge claim may have been waived by voluntarily agreeing to the lien (if the lien was voluntarily agreed to).
If the lien is from a judgment, then she likely can't contest it now.
A lawyer would review the facts and could tell your mother's friend what her options are, from saying "pay me the whole thing plus interest, you don't have a leg to stand on" to offering to take something less.
No more lawyer stuff, no more political stuff, so no more CYA