When turtle shells shed, all that's supposed to shed is the very thin, translucent top layer of shell. When scutes are retained, it means that the new layers continue to form underneath the old, but the old ones don't pop off like they should to make room for the new ones. Thus, layers of shell pile up. The problem with this is that if scutes are a little bit loose but don't fall off, bacteria and fungus can start to grow between the layers and the shell becomes infected.
I can see layers on your turtle's shell like rings on a tree trunk, so it does appear that she's retaining scutes. The shell looks pretty healthy at this point in time, though. How does her plastron look?
To help her shed, make sure she basks a lot under a good UVB light bulb and when she basks, she must dry out completely, top and bottom. Also, be sure she has a good, balanced diet that includes food containing vitamin e, which helps a shell to shed. Here are some good foods:
Tomato
Sweet potato
Turnip greens
Blueberries
Apple skin
It does sound like she's growing too fast. It's not healthy for her to do that - it puts a strain on their organs that may shorten her life. Here's a good link on turtle nuitrition. If you have any questions about anything you read, please let us know:
http://www.redearslider.com/index_nutrition.html
She's very pretty, by the way!
