Unknown mutt... help on what to answer?

Just put "mix" and if they ask just say she is a mutt and is mixed with a couple breeds. I honestly think it is because a lot of places like that won't let certain breeds in because of stereo types on the breed. When you look at her there should be characteristics of one breed that are obvious, for example if she looks most like a yorkie or has yourkie features then you would be fine with "Yorkie mix". ;)