Her given name is Kasen; her family name is actually printed twice; first as Ibara, then as Ibaraki.
All that happens in the first chapter, apparently, is Marisa and Reimu talk about her, something else happens, and then she shows up and a little bit of dialogue. (And Reimu has the best evil expression at some point.) Based on that, 2ch already has her pegged as Suika's ex-girlfriend - the comic has been out for not even a day and the great yuri machine has already started turning its wheels ...
Also, Febri only comes out every other month, so no more Kasen until the end of September :<