it can be quite common for a lot of children to want to stay a baby when there is another younger sibling around,she figures you are spending to much time with her brother/sister.
First,lets find out for sure where she stands,have you tried the naked method with her?
when she first gets up and changed in the morning,let her run around the house for a couple of hours naked,this lets her know what happens when she gets those feelings.
then stay with the cloth trainers and plastic panties,even when going out.it may also just be that type of potty,see if next time you are out if she see's one she might like.
I will wait till you let us know if any of this works before going to the three strikes method,I normally only use it for the stubborn over three year olds,but have at times needed it a bit earlier.
Please keep us up-dated on what you try and her responses.
tonya003, Hi and welcome to the Toilet Teaching board.
I agree with the previous poster, allow your DD to have some naked time, at least from the waist down. If you don't want to do that all day, then pick a time, morning, afternoon, or evening and go from there.
Please keep us updated on your DD progress.