Agree with what Maud said .. it has to be the best that the Brownie can do. I have very different expectations from a 7 yo compared to a 10 yo one. I'd chat to her about how she made it, where the idea came from, why did she that material, etc (basically weeding out the "Mummy made it" ones!).
As long as the brownie shows me the evidence of what she has done, I normally pass them as some of my brownies have additional support needs so what they are able to accomplish compared to some of my very artistic older brownies, then it's the effort and her delight in what she has created.
As long as she gets it signed off by someone in some way qualified or employed as an art appraiser/teacher, it will be good enough (they usually consult the criteria in the brownie badge book). Badges are generally more about effort than results I found.
Dd's got all excited about brownie badges. She's been doing musician with her piano teacher so I feel she'll sort out the standard. The other one at the moment is artist. She's been doing a collage and working away at it. Only she's got a bit excited about using different bits a d bobs and maybe not thought about how it all works as a picture! Fine by me-just glad she's enjoying it. But I don't want her to bowl up with her artwork and be told she hasn't passed! Is it the doing or the standard that'll count?