Ahh. Interesting bit of clarification. In either case, it's hard to argue as everything is theoretical at this point. Maybe they could not have justified taking on your project at all if they didn't farm it out to this freelancer.
So, for your budget (and I'm way over simplifying here) you could have gone elsewhere and gotten work more or less of the caliber of this person working through a lesser firm, or gone to this name-brand firm where the work would not have been done by an a-lister, but the project management and creative oversight would have been handled by them. Theoretically, they would have ensured an outcome on-par with their reputation, even if they potentially had to do some internal re-work if her output wasn't up to snuff.
This sounds, to me, like the scenario where the design firm was trying to expand their business a little bit and was doing so on a trial basis, with you and her both effectively as guinea pigs. I've seen this work really well and really poorly. If their signature is at the point where it can be easily reproduced under guidance, then you missed a good opportunity. If their style cannot be implemented by anyone other than these 4 or 5 people, you got lucky.
If I had to flip a coin though, I'm guessing you gave up a good opportunity here...
