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.
"Don't it" is not proper grammar. The correct form is "doesn't it".
It is proper grammar to say, "I bet you".
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.
Take a shower or a bath
This is simply because people do not want to take the time to learn proper grammar and spelling, or use it, when asking a question. Others haven't learned the proper grammar or spelling yet.
Most shower curtains are 70x70.