All are ok and natural?
(I mean she is nice, kind, gentle etc.)

She's quite the lady
She's a lady in the real sense of the word.
She's a gentlewoman in the real sense of the word.

Question

All are ok and natural?
(I mean she is nice, kind, gentle etc.)

She's quite the lady
She's a lady in the real sense of the word.
She's a gentlewoman in the real sense of the word.

Answer

Hi Pelin,

While I agree with answer below that these are correct sentences, I would like to add that none of them are common.  At least not among people my age (I am 29).  These all sound very old to me.  I imagine my grandmother using these phrases.  If you want to sound more natural I would recommend using something like "she is such a kind woman."  To me that sounds much more natural.  Best wishes.

Answer

All are correct.
The tone is slightly different.
Sometimes, "She's quite the lady" would imply that she is acting like a lady in a certain situation.

The other two would imply more that she has the qualities of a lady or gentlewoman within her, all the time.