Can't fool this kid

Tia has been potty trained for about 6 months now, except at night. I have always put a diaper on her at bed time and it hasn't been an issue.
Now for some reason she is resisting the diaper, saying she doesn't want to wear it and that she isn't a baby. I asked the doctor what to do. He said she is expressing her independence and need to be the 'big girl' which is common at her age. Especially since there is a 'baby sister' in the house. He said it will be quite some time before she will be able to wake up dry and although she continues to need a barrier at night, it doesn't have to be a diaper.
He suggested "Pull Up's", training pants, or "Under jams" and to let her know that they are just for her and not her sister.
I have always thought of these things as a glorified diaper and just another way for the diaper industry to continue making money. Well, I broke down and we went shopping. Tia and I picked them out (the package was pink with Princesses). I called them her "special night time underwear".
That night I pulled one out of the package, she looked at it and said "Mom, that's a diaper!". There's no fooling her, no matter what we call it, it's a diaper.
She's absolutely right, but she's just too darn smart!