Simply "I'm going to shower." would work. Have a shower makes more sense. It is hard to take a shower. If you take a shower any place, you just have a bucket of water.
However, "take a shower" is the common way of saying it, and is considered correct.
'In the shower' would be correct as the world 'shower' does not strictly define the shower head.
"She did not have" is the proper grammar.
It is proper grammar to say, "I bet you".
"Don't it" is not proper grammar. The correct form is "doesn't it".
no, that is definitely not proper grammar.
No, it is not proper grammar. The correct phrasing is "you and I."
What was there is proper grammar.
It is proper grammar.
There are many grammar practice websites that will help people learn proper English grammar. These are necessary since many people have no idea what proper grammar is these days.
yes
No
It's you are, you is is not proper grammar.