Cat Health problem

My Mum's 14 year old cat has been losing weight for the past few weeks, but has been much more noticeable in the last fortnight.

Apparently she's eating normally, or actually slightly more than normal. Her coat has gone quite dull, but she's still really active.
What could be going on? Or is it normal for older cats to just loose weight?

CongletonVet - any chance you know of the top of your head what might be going on.

Matt