Annette, formula milk is a more highly-processed product than cows milk - formula is cows milk, of course, with the protein partially broken down to make it more digestible; with much of the fat taken out of it and then calories added again in the form of vegetable fat; with some added vitamins (because some of the vitamins are removed when they remove the fat). Those are the main differences.
This all makes it more digestible and more suitable than cows milk for a young baby, but by the time a baby is a year old current guidance is that full-fat cows milk is fine and nutritious as a main drink.
Maybe ask again at the clinic what to do? Use formula if you want to, of course, but it seems a hassle! If she does not like it (and the fact she refuses cows milk indicates she might not) then you could ask about calorie dense solids.
You can also ask how seriously the weight gain should be taken - usually babies don't lose weight, of course, but maybe this is just a minor blip and she will regain what she lost. Could even be the scales, or incorrect reading, or incorrect writing, or incorrect translation from metric to imperial.
At eleven months (assuming no other health issues) a balanced diet with some cow's milk - if you want - will be fine, or don't bother with milk. By eleven months my DS was just on a balanced diet, and he did have serious health issues earlier which he had recovered from.
There is so much marketing pressure about what is suitable for babies, seriously, its just to get you to spend money its a load of B**
Ah I see, I thought you mean it's contaminated or something. Then stage 1 milk will be fine. Remember the tins actually have expiry dates. I worked out it was about the same price for me to buy a tin vs 5 cartons a week for nursery. And it saves me the hassle!
Why do you think formula would be better? Have you see the ingredient list? And if you don't like cows milk, then, are cheeses and yoghurts ok? Surely they are still the same thing?
For what it's worth, DD was given cow and gate carton to take to nursery when I went back to work at 7mo. She stopped taking them by 9mo. And she started cows milk at 11mo. She doesn't drink a lot of it until well over 1 year old.
At 11 months I would offer cows milk and extra food. Has she been ill, has she lost weight or has weight gain slowed down? It is pointless to give formula for 4 weeks and then switch. Also means no need to sterilise.