kaled - 1:33 am on Jan 31, 2011 (gmt 0)
If you go to the Companies House website, I think you can view the last set of accounts submitted (but I can't remember if they charge for this service - it's several years since I've done this).
I would not hire a lawyer, not yet anyway, simply acknowledge receipt of the email and say nothing more whatsoever - at the very least you'll confuse her and wind her up a little bit. Even if she chooses to hire a lawyer, you are not obliged to do the same or to fight the case, but if she does, you will have the satisfaction of knowing she's paying through the nose, even if you are not the beneficiary.
String it out, wind her up and make her suffer, but without putting yourself to any trouble or expense.