Basic strategy: Use one or only few number 1 slimes to chase the priestess towards a bigger mess of number 2 slimes. Keep it going continuously and try to predict where she will go next when spawning 1 slimes. Usually she will go into the opposite direction. But it can happen that she will change direction if you put too many number 2 slimes on one side and too few number 1 slimes on the other.
She can also get stuck in a corner. If that happens just let everything die and start over.
I don't remember these so well, but probably focus on upgrading mostly slime 2 first. Also upgrade unit amount after the first round to get more exp. Upgrade number 3 capture slimes late, only when you start getting her to low hp.