The eggs your broody has sat on for 2 days will hatch 2 days earlier than Dolly's eggs, and yes your broody will be forced to abandon Dolly's eggs to tend to the early hatched chicks. You can have an artificial incubator ready to go at that point if you choose to go that route.
Since Dolly's eggs are very important to you, I would pull the eggs your broody was sitting on, leaving her with only Dolly's. However, unless you have an idea how old the 8 eggs are, there is a risk that one or more eggs will turn rotten and explode under your broody. That only happened to a broody hen once, before I understood how important it is candle eggs. It happened 7 years ago, It was the most disgusting thing ever, and I've made sure it never happened again. Dolly's eggs are beautiful, and hope you have a successful hatch.