Her first rate was faster. The 10 minutes with a change in elevation of -200ft.
In order to solve this you need to have the same minutes. In this problem, I just simply took the 10 minutes and the -200ft and doubled it. Now both rates have 20 minutes. The first rate would have gone -400ft in 20 minutes while the second rate was only -300ft in 20 minutes. I hope this wasn't confusing, and I'm willing to explain more.