I would suggest using grain free products. Also no corn!!
Pumpkin based would be good as well as sweet potato.
The thing is, for example, using oatmeal would be good- but I also know two people who have bullies allergic to oats!! Peanut butter- another gummy treat- but recently found out that miss bailey is allergic to peanuts. So you never really know- that is why I say to stck with pumpkin and sweet potato as your main source of ingredient.