I would do as Catlady suggested; not Laura (sorry, Laura). There is no point in having any contact with the company, it will open the door (or the can of worms). Just advise the client you are no longer with the company and she should now contact Mr. X at (phone number, email address, or both).

I'm not clear as to how the client contacted you. You aren't in the office. she has your personal email address???? If not, WHY are you checking your work email? Just put on an automatic reply saying you are no longer working there and they should contact .... as above!