Pam, when we had our Rottweiler she used to drool white foam at the mouth and then she would vomit, but this was as soon as she started riding. Our Vet said some dogs just get car sick and some don't, I don't know if there is any medication you could give her.
We just stopped taking her, so far we have been very fortunate with Perry and Daisy, they love riding. We have to be careful with Daisy if she gets to upset, like getting shots she gets nerved up and vomits, but we have some medication to calm her and a special diet for a few days too. Good luck I'm sure the Vet can tell you if Bella will get over it with time.
Jackie

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