The populations of elves at the end of the Third Age in Eriador can be broken into three groups. The elves of the Havens with Círdan, the elves of Rivendell with Elrond, and the Wandering Companies who visit those places but don't reside there.
The Havens would have the remainder of Círdan's original folk (the
Falathrim) as well as the remnants of the survivors of Nargothrond, Doriath, Gondolin, etc from the First Age who did not depart oversea after the War of Wrath. So, likely predominantly Sindar, but with the mix you'd expect in a port town
.
The Wandering Companies are mostly Noldor, I think, as Gildor certainly is and his group seems representative. But perhaps not, as Frodo does seem surprised to see Noldor [High Elves] in the Shire. So, one could make an argument for other wandering companies (even perhaps Avari [Silvan], though that seems...unlikely). We are told that we don't meet any elves who speak a Silvan language during Lord of the Rings, and even the elves of Lothlorien are speaking Sindarin with an 'accent' that confuses the hobbits.
The elves of Rivendell are the remnants of Eregion (the Noldor land ruled by Celebrimbor) and Gil-galad's group after the Last Alliance. Thus, Rivendell is predominantly Noldor, and if anyone were to claim the title 'High King of the Noldor' in the 3rd Age...it would be Elrond. But he does not, for the obvious reason that there is no longer a kingdom left for him to be king of, and because, depending on how you reckon inheritance, his mother-in-law Galadriel might be like, ummm....that title is mine, kthx.
So, the 'default' for elves of Rivendell is definitely Noldor. But with so many of the elves in the 3rd Age being refugees scattered by previous battles, one can certainly argue for other backgrounds. My guess is that we won't specify, and just let the audience assume she's a typical Noldo elf (born in Middle Earth) from Rivendell in this season. If we decide to bring her back later, we can give her a more interesting back story at that time.