Does she stay in the classroom when you do a group lesson or is she asking you to take the students out of the classroom into your speech room? If the former, is it possible she's using you for an 'extra' planning time? If the latter, you can't do it!
I do push-in language lessons once a week into each of our 5 self-contained rooms. Not all of the students have speech IEPs. And the push-in time is not included in my speechies IEP minutes. OT does this too. This has been the first year I've been able to do this. If I were to get a few more new students, I might have to cut out those push-in times.
These times arenot an extra planning time for the teachers. Our union contract is very specific about the # of minutes per day of plan and lunch teachers get.
I always tell teachers they can go do whatever (make copies, bathroom,) during that time because I am nice. : ) They are in and out and frequently use the time as extra instruction time with a student or two.
Smile,but be firm and don't bear this alone. Ask someone else, like your dir of spec ed for help with this.