[ownedbycats]

It may be that to her the other dogs in the class are "known" quantities. She has seen them doing the same things for the same cues (probably not perfectly, but reasonably reliably). She now knows how these dogs will act. Strange dogs are still "unknowns" who may or may not react in a way she can predict. (This is just a guess mind you - wouldn't it be nice if we could just ask what was going on inside those fuzzy little heads, and get an answer?) It may also be that in class they don't meet head on until they are ready. On a trail, they are almost forced to meet face to face right away, instead of approaching at a less confrontational angle as they would in a more open setting. I read somewhere, and I can't remember where at the moment, approaching head on is confrontational for dogs, a sideways approach is more polite and preferred by the dogs unless they know each other, are young, or unsocialized.