The seminary that is called Ateres is Ateres Bnos Yerushalayim and it is in EY (in case you can’t tell from its name).
If you want to know more about it, it’s best to ask girls who were in seminary within the past year or two, since these things change all the time.
Any information I have is slightly out-dated. There is not much I can tell you anyhow. It’s a Bais Yaakov seminary but on the more open-minded/left-wing end of the Bais Yaakov seminary spectrum. The last I heard they were getting a mix of girls including more modern Bais Yaakov girls and Bnos Rochel girls. The girls whom I know who went there loved it! They are more open-minded than most Bais Yaakovs. I believe it is less pressure than most seminaries and has more hashkafa (but you might want to check that out).