After thoughough-ish investigation it looks like the Heinz Nuture are all Casein dominent and the Karicare ones are Whey Dominent (I didn't look at the S-26 (is that right?) as it was more expensive than the Karicare HA she is on now and would defeat the purpose).
The plan is to buy a tin of the standard Karicare follow-on and try her on that whilst we still have 1/2 a tin of her special formula just in case we have any issues (we haven't when I made her bottles with the sachets for the past 2 days - is that enough for a reaction to show?). The good news is though (sorry if TMI but this is an ongoing issue we have), that she has pooped 3 times in 2 days!
She hasn't done that since she was BFd!!!
I had to laugh this morning though when she was standing up at her safety gate "talking" to me in the kitchen, she stopped almost mid-sentence, seemed to semi squat and filled her pants!
Charming little girl!