Yes, it sounds like it is high time to take over her finances. Has the POA been registered? If so, then you are good to go, otherwise it will need registering before it can be used. The bank will indeed need to see the original paperwork, so I would book an appointment to see her bank manager, take the paperwork (they should photocopy it and give it back - make sure you do get it back) and 2 forms of ID. They can then sort out her account keeping the same account number, but giving you a card and cheque book in your name which you can use on her behalf.