Look for tiny red (or sometimes brown) creepy, crawly guys on the underside of the leaves--a magnifying glass helps. To the unaided eye they will probably just look like a few tiny specks (perhaps very few). These are spider mites. The easiest way to treat something this small is to spray the underside with a forceful spray of water. Often a handheld sprayer adjusted right is enough. Repeat every few days until they they seem to be gone and isolate them from other infected plants.

Thank you very much Mark. I've been doing as you said and it looks like the little buggers are going away! Hopefully my Lady Margaret will start to recover now :)