I think you should definitely address this. My main concern would be the elopement risk. Now that she is in gen ed for more than one hour, are they addressing this issue in the new environment? It's one thing for a general education teacher to make sure an elopement risk student is safe for one hour; it's a whole other thing when it's six or so hours. (And what about lunch and recess and specials? I'm gong to assume those have been taken care of in the IEP...)
I wouldn't want to wait until the scheduled IEP meeting in September (unless it's scheduled for early in the month). You need some assurances immediately about her safety.
I would approach the subject (and a request for a meeting ASAP) in the same manner that you worded this post. How much you like all the teachers, are happy she's can be in gen ed more, but due to past experiences, you are fearful this will not last and want to make sure the teacher is prepared for the possibility of elopement. You also want to request that you be notified of any placement changes in the future prior to implementation - just so it can be discussed with you ahead of time. Stress the safety issue - schools shouldn't think a parent is "crazy" for wanting to make sure their child is safe.
Soft language can be used now. But if that doesn't work, I am happy to draft some stronger language for you!