Skill's relative. It's pretty hard to take a driver and predict how they'll do in a different car.
Case in point, Michael Valiente, a Daytona Prototype driver, had a podium finish at VIR this year. The next weekend, he was out racing karts with us at Infineon, and he got clobbered (he wasn't in my class).
Meanwhile, Memo Gidley, a regular at our meets, does very well in the kart races, but not so well in his Prototype.
IndyCars are pretty darn big for Formula cars. As much as they look similar they are very different to an F1 car. Maybe IndyCar does not suit Danica's driving, but F1 would? Impossible to tell.