M.R.
This is usually a very bad idea. It is especially bad for kids with disablities. Since your daughter has just had her evaluation (I assume) from early intervention to school age, and she will recieve approrpirate intervention services based on that evaluation. I understand your hope, but it does not work that way (the data does not support that feeling you have.)
Go to www.wrightslaw.com and scroll down on the left side of the page and click on retention. Most of these articals will be from the perspective of parents not wanting to retain, but you really need to read about the realities of how kids do when they are retained. It really seems like your logic would work, but sadly, it does not.
I have been there, twice. Once with a child who is MR. The data is correct, and both my kids were huge surprises. If you don't set the bar, they can't jump it. She just might.
Let me know if we can talk further. I have worked as an educational advocate too, so I have seen very many cases and might be able to help.
Check out the sources. It may not "feel" right, but trust me, it is.
God Bless,
M.