N.J.
I think its fairly typical to be afraid of the big toilets. You don't need to buy a portable toilet, just use the training one you already have. I still bring mine along on long road trips for my 5 year-old daughter. I'd rather have her use that then some gas station potty. What really worked for her at three were the little toilets. The Thousand Oaks mall has them by the play area and they also have them in the Baby Center at Disneyland. She would joyfully leave her playtime to visit the "little potties". Once she's more comfortable with these, she may be ready to move onto the big potties.