Cheers for the good wishes, folks.
Basically she got a throat infection about 8 weeks ago, and her neck developed a large swelling. It was assumed to be something to to with the infection but it turns out to be an unrelated lymphoma. And it'll be another fortnight before they know the severity and if it's Hodgkin's / Non-Hodgkin.
Hopefully it's nothing too serious and is exacerbated by the immunosuppresants she takes - she's just had her dosage reduced which will hopefully help. I think the long-term survival rates are excellent for most forms of lymphoma for her age (about 100% for Hodgkin's), so fingers crossed. There's also a worry she'll lose the kidney, though.
Best wishes to your Dad, Malc.