I personally think people are missing a big point that James Camerons film was a work of FICTION based on the real disaster - Rose, Jack and a whole host of fictional Characters were intermingled with real life people.
And therefore I believe In James Cameron's fictional version of Titanic, more than 4 first class women were supposed to have perished - I mean Rose was believed to have 'perished' before she turns up as an 101 year old. I think James Cameron used a huge helping of poetic licence across the whole thing - and probably made a creative decision to have more women die supposedly in the disaster.
So I always took the floating woman to be a first class Passenger who never existed in real. Probably someone who refused to get out of bed until it was too late and caught in only her nightdress didn't make it far from her room before downing - something that could have been very plausible in an alternative universe!
There where a myriad of fictional 3rd class passengers like Cora and her family, Helga Dahl and her family, Tommy, Fabrizio - so why shouldn't there be extra fictional
first class passengers we never saw the backstory for who perished
Also James Camerons version there seems to be a lot more women perishing in the sinking scenes (of all classes) then there really were (I think there were 'only' about 110-120 women who actually died on the titanic) but the 1997 film makes it look more like 300-400 - all in the name of looking more dramatic.
Also note the ending dream/death scene where old rose goes 'back to titanic' - there are a number of 'first class' looking women gathered on the staircase - and I do believe JC was suggesting those people were the ones who died on the titanic - as you don't have Ruth, Cal, Molly or any 'survivers' etc returning for that scene.
I mean I didn't know only 4 first class women died in real life until researching some years after watching the film, and if asked after watching the film how many first class women I thought had died - I'd have said 20 or 30. So I think JC and other film makers often buy into that ignorance of the general viewer!
So the floating women = first class but fictional
NB, Trudy, Ruth's maid is a good example of this too, JC kills her off in the film (we see her sliding down the deck during the sinking) and as a first class servant, she'd probably have been listed as a first class passenger - upping the first class female death toll +1 in the film....... so it's easy to see how in JC's mind their would have been more!