The residents of the Scarlet Devil Mansion are numerous and infamous. The known list includes Meiling, Koakuma, Patchouli, Sakuya, Remilia, and Flandre. But there's one more person that I believe resides there, and that person is Kana Anaberal from PoDD.
How is it possible for a PC-98 character to be a SDM denizen? Quite easily, actually. Embodiment of Scarlet Devil happened in 2002. In its character notes on Reimu, it states:
Chronologically this title is not too far from the previous
title, thus her age stays the same as before.
So it was less than a year after Mystic Square, if we can trust ZUN. But in
Aya's article on Lunasa, which takes place in
1998, it mentions the Scarlet Devil Mansion explicitly. So the Mansion didn't just poof into being for the events of EoSD, it's been there for a little bit. This also implies a little something about the Vampire Incident, but we're not here to rehash that noise.
Now, let's talk about Kana herself. In her PoDD profile it states that she's a poltergeist created by "a mentally unstable girl," and lives in "an enormous Western-style mansion." Now, there are a number of Western type buildings in Gensokyo, including Alice's house, the Prismriver manor, and the SDM. But Alice's house isn't big, and Layla specifically created shades of her sisters. Plus, Flandre has been referred to as not being in her right mind more than once.
Her situation in PoDD, specifically, is that "lately its owner has gotten used to her and won't pay her much mind, so she's thinking of moving." Well, yeah. I don't think it would take that long for Remilia to become accustomed to having her around, especially considering all the other supernatural stuff that happens around there anyway.
As for the maid dress she's wearing, that's because she's probably been drafted as an SDM maid. Sakuya probably still does all the work anyway. Kana may be even less reliable than the fairies, since the purpose of a classic poltergeist is to toss stuff around, make noise, and try to scare people.
It's probably just a coincidence that someone named after Cape Canaveral lives in a place where they shot off a moon rocket, but I wouldn't put it past ZUN to do this deliberately.