I think
Mabel is cute in an on-someone-else's-kid way. I'm not fond of
Mabel Emily. It just kinda slurs together.
Mabel Sarah is nice though.
I think
Mae is nice too but with
Mabel being only two syllables I don't think it has a need or use for a nn.
“It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.”
~Mark Twain