Is she going into kindergarten or first grade? The 6 yr olds in kindergarten have accidents ALL the time. My son just finished kindergarten. He himself didn't have accidents, but his BFF would have 1 - 2 EVERY day even though he used to not have them at all. Every kid in kindergarten has to have an extra set of clothes at school, and most use them often!
It seems to me that she is starting to have an accident and then catching herself and stopping it or not quite making to the bathroom in time and getting her underwear wet before she can get them down. But, she is embarrassed to tell you. I seem to recall my daughter having little episodes like this too at that age. SHE WAS MORTIFIED! AND ..... she had no clue what was happening!!!! She didn't realize she was just having little accidents, because she hadn't had them for years before.
Like someone else said, their bodies often grow faster than bladders can keep up with. My son (6) will go forever staying dry at night and then have a whole week of bed wetting. Then go months again dry, then another wet spell.
Crazy pediatrician! I love our doctor. He always starts with the simplest explanation. Cool and feels weird is exactly how I would describe it if I had wet pants!