English help!

Depending on context, the 초 one is fine. For instance, if she was at a swimming class where it was shortened to simply "swimming" then that is fine. But for the first one, idk, I think it would need to be re-worded a little, but I will need to know what context 당신 are using it in...

당신 could say;
He/she was happily swimming.

or;
He/she was good at swimming
He/she was happy to swim

hmmm...

Non native speaker huh?

I would say "He/she was happy while he/she was swimming."

OR

He/she liked swimming

For the 초 oneL

He/she was very happy while he/she was swimming.

He/she was good at swimming

He/she enjoyed swimming.

There's a lot of ways of saying it, but the way 당신 have it sounds funny.

Im not much good in english,sorry...