Yikes, $7,000 seems pretty steep
I personally wouldn't hesitate to go with the less experienced orthodontist. She finished her residency, so she's fully trained and up on the latest techniques. And if an orthodontist makes a mistake, they have plenty of room to correct. If I had to have brain surgery or a heart operation, that would be a different story.
The office I go to has one very experienced orthodontist, but the one who I've seen the most so far is fresh out of a 2 year residency program.