I assume that you mean that the lady is one of two attorneys named in the LPA (rather than her having appointed someone else as her attorney).
If so, is the person whose affairs are covered by the LPA still currently able to make his/her own decisions? If he/she is then they should complete a partial deed of revocation and send it to the Office of the Public Guardian. (It simply means typing out a few sentences, signing it in the presence of a witness, getting the witness to sign it and posting it. No form is required and no lawyer is needed):
https://www.gov.uk/power-of-attorney/change-your-lasting-power-of-attorney