I have heard, too, that when kids are harsh with their toys in that way - they are in charge, and the toys are "under" them, that they often work through things that are bothering them that way, and express things they couldn't say. And then, too, sometimes it is just play :-)
To some extent the behavior your daughter is displaying with her peers is not really unusual for the age. She will likely make adjustments as she moves along and receives feedback from her peers about what they find acceptable and not acceptable. Unless you witess her mistreating a peer, it's not something you need to involve yourself in apart from the usual guidance that parents tend to offer. At this age children are figuring out where they fit in, so to speak, and the peer relationships are worked out in the context of activities. So it is encouraging that she is engaged with her peers. It might be helpful for her to be exposed to different children and within a different structure than she's experiencing at the after school program, but at the same time there would be no pressing need to make a change. The important thing is whether she's happy with the situation and has some contact with same-age peers. Likewise, I would not suggest you interfere with her solitary play - it's fine. Relative to parent/child interactions, she may be quite sensitive to indications of displeasure on your part, and she may tend to regard routine limit-setting as rejecting in some way. If she is acting in a disproportionate way it would be useful to have brief exchanges with her about 'where she stands' with you. At this point it does not sound like any professional intervention is required, but keep an eye on the peer relationships to be sure she isn't alienating herself.