10 miles isn't that far in the horse mind. It is pretty likely that she will end up back at her former home unless she finds a more interesting pasture containing horses between there and home. Most horses have a miraculous sense of direction and can find their way home from a very long way, even in a strange direction. Just to be on the safe side though, call the local authorities, animal control if they have one, drive around the neighborhood looking for prints and piles of fresh manure, talk to neighbors to see if they have seen her and which direction she was headed in. If she doesn't turn up before tomorrow, then they might want to put up fliers with pictures in local feed stores, grocery stores, tack stores, vet's offices, anywhere people go. Make sure that all the local vets know about the missing horse in case she ends up injured and a stranger brings her for treatment.
Of course, all that is precautionary, my bet is that she shows up at her former home.