To say someone is stone is to say that that person does not permit sexual touch, esp. penetrative, upon their person. In other words, if a stone person is having partnered sex they would be the pitching, not the catching, partner. (See Stone Butch)
In common usage, Stone Femme has two quite different definitions:
The grammatical parallel structure of stone femme / stone butch would logically indicate that the femme, like the butch, is uninterested in receiving sexual touch. Thus, femme-who-is-stone.
*The other possible meaning, femme-of-a-stone-butch, simultaneously implies a denial of the possibility that a femme might be stone (by supplanting the parallel term with an identical term with an opposite meaning), and if read the right way, implies a type of relationship ownership, as in "Mrs Stonebutch". This meaning is deprecated.
A Stone Femme usually partners with and is attracted to a
"Stone" can also be used to refer to butches who prefer to top and not be touched sexually themselves.