Regarding slightly differing address info, I'd imagine Jack's information re the ward name is correct. I was told to simply use 'The Oncology Ward' Best to go with Jack's 'Podium 1 ward' I think.
However, 'Stirling' is most definitely spelt 'Sterling' for I took the address details from the hospital's own website. It also includes'Greater London' in the address, as you will see in the link here:

North Middlesex Hospital - Address & Contact details

Cards to:

Diane Easby
Podium 1 Ward (Oncology)
North Middlesex University Hospital Trust
Sterling Way
London
Greater London
N18 1QX

Tel: (020) 8887 2000

Good news about the cats, Jack. That alone will take a lot of worry from her shoulders, I hope.