Awwww bless, it sounds like the whole cattery thing really wasn't particularly pleasant for Izzy!
Some cats take to it and some don't, if you're satisfied that the cattery cared for Izzy as they should have, then i'd put it down to her having had a traumatic experience - poor Izzy!
She's possibly eating like a horse now to make up for the week she was in the cattery and was too stressed to even think about eating!
I believe that cats attach themselves to places rather than people, however, because you were only gone for a relatively short period of time, she wouldn't have had time to settle in her new 'home' - the cattery - and she would have been delighted to see you when you returned! (Or should that be smell you? lol)
It's often said that you can move new owners in to a house and the cat will quite happily stay where they are! Also, cats have been known to travel hundreds of miles, on foot, back to an old home.
That's why we have to keep new pets in for several weeks because they'd just go straight back to their old residence, never mind whether the house is empty, or their 'owners' are 200 miles away in the new house!
So..whether they actually have a 'memory' such as we do, is pretty hazy.
Personally, i believe they remember what they want to remember!