Why Is this happening?My 4 yr old must feel so embarrased!?

It seems she may be making a conscious choice to pee whenever and wherever she has the urge. If so, this is probably a psychological problem. It might be worthwhile waiting to take her to a psychologist before putting her back into diapers if you can hold out a little longer. In the meantime, one thing you can have her do is to sit on the toilet every hour or 1.5 hours and have her empty whatever is in her bladder.