The hormones of pregnancy (oestrogen and progesterone) act to cut your milk supply. Your body goes into gear to support your new baby. Sometimes toddlers go along for the ride and are happy with the new arrangement, because for them, it was about the relatinship, not the milk. It sounds like your little one wants the milk and will feed all day to get it if she has to. It's likely this time will be a period of adjustment for her.
For a good read, check out "Adventures in tandem nursing" - might be available through your ABA group library, and is available through ABA's online store
Makes total sense. DS only feeds when he's tired now. I still have milk but I doubt it's enough to be anything substantial or filling for him and a certainly don't feel as full as I used to.