@davida50 My kid does a lot of opposition and her emotions are intense.
Taking your example of not wanting to take her shower.
First she needs to say it to me respectfully, if she doesn't she simply doesn't get what she wants.
I'll remind her she needs to speak to me gently because I speak to her gently, I'll acknowledge she doesn't want to take her shower.
Once she asked respectfully then I know the emotion is passed and the logic circuit of her brain are back.
I'll then ask why she doesn't want to.
That's the part where she listen to her emotion herself.
If the reason is acceptable like she wants to go finish her drawing first I'll let her go. If she doesn't do it after the next time I'll say no.
If she just doesn't want to then I'll just sit there and wait, she has less patience than I do.
Kids are an ever changing challenge.
Its full of trying stuff and seeing what sticks.