She's not ready. Its not her being "stubborn".... but its her body.
Toddlers, know in their heads what is going on and they may understand... but for a Toddler, 'knowing' something is NOT the same as being 'able" to do it. Thus the reason for tantrums at this age and in tandem with their emotions which are not even fully developed at this age.
Denise P. below gave good advice.
Once a child is truly "ready" for using the bathroom, they will. But even then there WILL be regressions or some days they are not perfect. And they WILL have accidents. Normal. So you have to accept that. Even 7 year olds have pee accidents.
And, keep in mind, that even if they are day-potty-trained... this does NOT mean that they are night-time potty trained. Night-time "dryness" and during naps, can even take until 7 years old. And is normal. Night time dryness is an entirely DIFFERENT ability. It is biological. Not the child being lazy.
The adult "expectations" are often too much, too soon, and expecting it to be too "perfect." Thus it does not work.
All the gadgets and gizmos will not work... if a child is not ready.
My kids, I never bribed them or punished. I just encouraged or went by their cues. My son, is 3.5 now, and only very recently has he been "ready" for pottying He even told me "IT'S MY BODY!"
Plus, you are going to have another baby. In my experience, this will not "make" an elder child potty train. They are dealing with your pregnancy and the upcoming baby and their emotions are not matured yet.
Even if a child is potty trained, seemingly... they will regress.... and this indicates in a child that they are "stressed" or unable to cope with external expectations upon them.
All the best,
Susan