Please don't label her "hyperactive." That's a medical diagnosis. Bear in mind, as you note yourself, she's a toddler and they are all go-go-go-- especially to a mom who likely is very tired due to having a four-month-old infant as well, right?
You seem to say her "hyperactivity" comes mostly during this one particular class, or at least that's where it presents an issue for you. This is a gym class -- how much time are they in circle time anyway? Shouldn't they be moving around in this class? Is she on the younger side for this class, or maybe just a little less mature than the other kids, hence her tendency to ignore "you must be in this one spot" rules? It all sounds pretty typical to me.
I think maybe it upsets you that she is "misbehaving" in these classes but frankly if the teacher is any good and in any way experienced working with kids this young, it does not matter. The teacher should be able to handle having one kid (or several) who are not doing exactly as they're told -- there are kids twice your daughter's age who do worse that she's doing. If the other parents are giving you glares, ignore them -- believe me, somewhere else, their kids are moving around when told to sit. Worry less about her not being perfect in this one class. If the class doesn't have her moving around enough, find a different one that really lets her burn off energy better.
If she is sitting still through a show she is doing fine. I hope you mean a live performance -- try her at a live show instead if you mean TV. If she can sit through a kids' puppet show, etc., she really is doing well for only two. And if she gets up and wanders around -- well, she is ONLY two.