You've changed the comparison.
In the first post it was
I'll vs. I'll be ---ing.
In the next post it's
She'll vs. She's ---ing
Did you intend to change the comparison?
In any case:
I'll be attending. (In my mind I can already see myself there.)
She'll be throwing a party. (In my mind I can already see her preparing for the party, greeting the guests, etc.)
I'm attending. (I have already scheduled myself to attend.)
She's throwing a party. (She has already decided to throw a party and has told people about it.)
I'll attend. (Since this is first person (
I), it is like making a promise to attend. If I don't attend after saying this, I have broken a promise.)
She'll throw a party. (This may vary in meaning according
to context. We may be speculating on what she will do in the
current situation.
Will she throw a party? I don't
know. I think she may not have time to throw a party. Or,
maybe she does have time. If she has time, she'll throw a party. -- Often there are unstated conditions behind a
will statement.)
CJ