Hi there! It can be hard to find just the right balance of solids and formula. Keep in mind that formula should continue to be her main source of nutrition for several more months. She should get 26-32 oz of formula per day. Solids amounts really vary quite a bit, so your best bet is to keep an eye on her formula intake and go from there. If she's taking less formula or is losing interest in her bottles, cut back on the solids. Does that make sense?
As for introducing the 3rd solids meal, that doesn't necessarily mean she should start taking less formula unless she's eating more than 32 oz per day. It's really up to you and her when you start the 3rd meal. If solids have been going well and her body seems to have adjusted to it, then you can start the 3rd helping whenever you'd like. HTH!