Is the team willing to have her in mainstream for art, music, and/or lunch/recess (this would be least preferable because lunch/recess is more unstructured)? I think the goal is to move her slowly, not just have her in either self-contained or fully mainstreamed. By moving her first for art or music, you have her in a reg ed setting but the academics shouldn't be stressing her out. Then you could move on to an academic subject that she likes and/or does well in. Set her up for success.
Not knowing what the "little things" are, it's hard to know whether they're being overly severe. It is highly unrealistic to expect "perfect" behavior in any setting, from any kid. If her "little things" are comparable to things kids do in the regular classroom, then they should not be held against her. Just because she's been in a self-contained placement, she should not be held to a higher standard of behavior than the kids in mainstream. At the same time, it is reasonable for school staff to hold her to a similar standard of behavior as her peers if she wants to move back into mainstream.
If she does not have any social/emotional goals on her IEP, it's time to beef up the IEP so that the SD is addressing that issue.
Finally, IDEA guarantees free and appropriate public education in the least restrictive environment (FAPE in LRE). Obviously, a self-contained classroom is pretty restrictive. I also believe (and this is just my opinion) that some SDs tend to think it's easier to keep kids in self-contained than it is to provide the supports to move a student back into a more mainstream setting. You may have a fight on your hands, but I think it can be done. Another thing to consider is that junior high is looming - far better to work on reintegrating into mainstream on the elementary level rather than at the jr. high level. Do you know what their plans are for her in terms of placement in jr high?