Ramsgate was a...plot device! ;-)

Seriously though......

Both Colonel Fitzwilliam and Darcy would have had to agree to her spending the summer at Ramsgate. She has finished school ;

About a year ago she was taken from school, and an establishment formed for her in London; and last summer she went with the lady who presided over it to Ramsgate;
Chapter 35

and therefore is just about to "come out". I get the impression this is a holiday before Georgiana is launched onto the marriage market, if you like( but that's only my opinion and you don't have to agree with me)

Perhaps Darcy thought it would do her health good- spending time by the seasisde, regarded as recuperative and good for you in this period of time( more on this later in the GR).

I get the impression that Georgiana is a studious girl- she is very accomplished : even Darcy speaks of her progress on the paino (and harp) with "affectionate praise".Perhaps Darcy thoguth it would benefit her health to vist a quiet place by the sea where she could bathe etc etc.