Is this construction with dengan the typical way to make adverbs?
He stands up steadily is not accepted.
I think this is not talking about rising up, but rather standing fast.
you need to review this series of questions, sometimes only the present is accepted, sometimes only the past. There are several acceptable translations for these sentences.
Are there other ways to translate "mantap"?
This should be "Dia berdiri yang mantap."
The meaning should be "dia berdiri dengan tegap" instead of "mantap"
She is standing steadily
Is the same.
Have a look at this question Duo Lingo
since there is dengan word, shouldnt the direct english translation be she stands with steadiness