Every action has consequences, sometimes not the ones you are expecting.
I too suspect your mother is the anonymous tipster but doesn't want to admit it.
By attending a JC or even answering their questions, you are then demonstrating that you are accountable to them. Even if you did attend and answer their questions, they would likely still decide to DF you, even if you cry and claim repentance, agreeing to change your entire life to conform to their demands.
If you end-up being disfellowshipped, start to realize it is their club, so membership is entirely by their rules which may change as they see fit.
If your relationship with your mother is your main concern, also realize that it is entirely her choice if she disregards her relationship with her adult daughter, placing the WT cult above her own flesh and blood. If you were to give-in to conditions to be accepted, that will likely result in more conditions being added as time goes-on.
With regard to involving a lawyer, often the threat will be adequate, particularly if the threat is directed at the Elders personally, not at the Cong or the WT.
A legal threat will require the Elders to seek direction from WT but as the threat is not directed at WT or its assets (cong), then WT will often advise the Elders that they are on their own so they may not wish to proceed with the matter especial if you are not identified as a JW in your new area.
Since you no longer live within those elder's congregation territory, why would they wish to stick their necks-out as legal action would require a legal defense. If WT is not backing them, legal costs would be entirely at each individual elder family's personal expense.