D.W.
The bigger question should be should you even continue to employ this babysitter. If I felt like someone had no idea how to care for my infant (ie giving junk food "behind my back") then they would no longer be the babysitter period.
A 9 month old doesn't need leftovers, cupcakes and whatever else she is eating. Because leftover, cupcakes and whatever else she is eating hasn't been prepared for a 9 month old-without extra salt, sugar, heavy seasonings and fats. At 9 months old, food is simply for practice and breastmilk or formula should continue to be primary. If baby is being given food items like cupcakes that takes away from tummy space for valuable nutrition.
If it were my kiddo, I'd be preparing his "meals" and providing them to the babysitter and making it *very clear* that is all baby is to have.
At 9 months old you can introduce egg yolk. It is recommended that you wait until at least 12 months old before introducing egg whites because they can be highly allergenic for some kiddos.
Here is a great site with feeding ideas and amounts:
http://www.wholesomebabyfood.com/index.htm
Great, great info on this site about what the feeding guidelines are and why the recommendations are what they are. Also sample menus, recipes, etc.