I would take her to the doctor. I just read an article in a pediatric journal about a girl who had vaginal pinworms for 5 years! If she is complaining the most at night it is possible because that is when they are most active. Kids usually complain the most at night and in the early morning.
My pedi told me once that after potty training wipes can be bad because they are so drying. They are meant to take moisture away and clean the area which in a potty trained child can actually be overkill. They can also cause yeast rashes in girls because vaginas are self cleaning and it screws with the natural balance. I just stick with TP as a result.
Also are you using actual overnight diapers? We had rash issues after Pting from that. I needed actual overnight diapers in a size up.
Give her a baking soda or AVEENO bath, let her be naked under there, put cream on at bed and see what happens.
Likely a yeast infection. And um... as a pharmacist, I would hope you have a better idea of the risk/benefit of using Canesten cream for a couple days than your DH does.