Well if the MPI is confirmed and GI thinks she has reflux in addition and not just as a symptom, the why are they trying to make you wean the gaviscon from the bottles and use rice instead? If she has reflux then gaviscon is fie to continue using so why take her off of it? Bit odd, but maybe I am misuderstanding.
Instead of rice cereal you can get Carobel which is a thickener made for infant formula. Rice cereal can gloop up in the bottles and be a bit of a choking hazard but Carobel is specifically made as a milk thickener.
I second what Canwi says about reading the labels every time, but a good milk-free rice cereal is made by Organix, I found it only available at the larger Tesco and Asda stores but at most Boots, but I lived in quite a small town so that could have been a factor. Do check the box every time as things change. At the time I was using rice cereal for DS, Organix was the only milk-free cereal we could find.
You said that you have friends with LOs on Aptamil/C&G Pepti, but that sounds wrong to me...although it's been a few months since I was into formula and milk-free and what not I am 99.999% sure that C&G and Aptamil do not make a hypoallergenic formula. If they do I would be flabbergasted that you can buy it off of the shelves in the UK. That you say Pepti makes me think you may mean Pepti Junior? Pepti Junior is a full elemental formula, meaning it is 100& totally hypoallergenic - it is the same as a formula by another brand that is called Neocate. Both Pepti Junior and Neocate are available with a prescription and both are extremely expensive should you choose to buy them on your own. When we priced it to see if we could get some to bring with us to Germany when we moved it was 48 pounds for a HALF sized tin. Not something you can reasonably buy!
Aptamil and Cown and gate both make a milk called "easy digest" or "sensitive" (not sure which one uses which name) and it does say on the box that it is for babies who have trouble with milk proteins. This is NOT hypoallergenic formula. It has the milk proteins only very partially digested, NOT enough for a milk intolerant baby, so you should not try this for your LO! Nutramigen, although it does taste horrible, is really what your LO needs to be on (or Neocate, Pepti Jr, should GI decide, as it is MORE hypoallergenic than Nutramigen). Your LO will take to the Nutramigen sooner or later, esp as she is very young.
With the weaning time, most paeds and GIs will strongly advise that a LO with a milk intolerance be weaned no earlier than 6 months. The reason for this is because the intestine tends to be more sensitive in babies with food intolerances and early weaning can cause more discomfort and even intestinal damage. BUT you are right, in reflux babies often earlier weaning is advised....so in LOs with both reflux and MPI, it's a toss-up on what to do. In this case I would advise just following what your doctor says to do, which will probably be wait until 6months.
Does any of that info help???