Recent food change - causing sickness?

Hi, poppy was spayed about 2 months ago, as a result out vet advised to put her on calorie control dry biscuits. We weaned her off her usual food and she is now eating the calorie control biscuits mixed with a small amount of tuna. The biscuits are much bigger than her previous dry food and she wolfs down her food. she has started to be sick after her meal - usually just a small amount but the biscuits are still whole. Does anyone have any suggestions? I was thinking of breaking the biscuits up or mixing a drop of warm water in tomorrow...or is it maybe the food just doesn't agree with her? Any help is appreciated xx

Hi, she is 16 months and we currently feed her twice a day. We started off 3 times a day up until she was about 6 months old but since then it has been twice a day. We are feeding her eukanubu calorie control for small dogs and a forkful of tuna. I will try her on three times a day and singers crossed that will help. Thanks for your response