Rhea Silvia was the mother of Romulus and Remus, and so not a Greek goddess at all. Indeed, her name often appeared as Rea Silvia, and it is possible that the spelling Rhea was introduced by writers or editors who were thinking of the Greek Rhea in the entry above.
If she is Rea Silvia, then the first part of her name may be nothing more than rea, 'one accused', 'one condemned', perhaps referring to the 'guilt' of her giving birth to Romulus and Remus. (One account tells how her uncle Amulius 'exposed' the twin brothers after Rhea had given birth to them, and then imprisoned her; she was released many years later by her sons.) Silvia suggests 'of the forest' (latin silva). In an early version of her story, in which Rhea is said to be the daughter of Aeneas, she is called Ilia, after his homeland of Ilium (i.e. Troy).