It is impossible to tell how much exactly a hamster eats because they hoard so much so a change in her set up wouldn't really help.
I don't often weigh my hamsters and assess their health more by appearance and behaviour but will take them to the vet should they start to look thinner, appear lethargic or in discomfort.
Did you give your hamster a health check and check for any lumps?
Yes, i'd definitely leave the formula out, feed Bunny dreams only and supplement with things like dried mealworms and sunflower seeds.
You could check the ingredients list of the Beaphar and Science Selective pellets online to see if there is a difference and then opt for the one you feel is the most suitable. Ingredients can vary from country to country.
If your hamster continues to lose weight for no obvious reason it may be a good idea to get her checked by a hamster knowledgeable or exotics vet.