M.P.
Here is what I suggest:
http://nickisdiapers.com/catalog.php?category=16
I would do a pocket style so you can change the absorbancy level since it sounds like she needs a lot of protection. I would also get a hemp doubler or three because they absorb three times as much as cotton or microfiber does. You would place them under the microfiber insert though to create the optimal night time protection. Here is a link to one:
http://nickisdiapers.com/catalog.php?category=772
It will all seem like a steep price tag, but remember that they can be used for MULTIPLE children. If you are just using them at night, then I wouldn't suggest more than three. It's recommended to wash every 2 days to avoid stinkies. But you should know that a 4 year olds urine is more potent smelling than a 1 or 2 year old so you might want to rinse them each morning in your tub.
If you have anymore questions, feel free to ask me. I love helping people out.
also you can find a group on facebook where I admin and we love to help newbies out, even if it's just at night. It can be intimidating!
http://www.facebook.com/ClothDiaperingMommies
p.s. I was a bedwetter till I was 12 (thank you bladder that didn't grow as fast as I did) and I'm sure my mom would have LOVED these if they were around. lol!! Would have saved her TONS!!