Putting 4th grader in 1st grade classroom

A family I previously worked with contacted me about their daughter. This girl is identified with severe ADHD and mild mental retardation. The Resource Room she is now in takes her down to the 1st grade room to work on reading. This is where she is at academically but it is important that she be with age appropriate peers. She is very aware that they are having her work with kids much younger with her and is starting to shut down. Any ideas?