I made a mistake. It's Ishikawa Natsumi. Girls from PassCode, NECRONOMIDOL, Avandondol, Idol College, Mecha High, Kamiyado, Otome Shino, Houkago Princess, etc. are also in it but no "big names" like Terashima Yufu as far as I know.
This ridiculously bouncy girl from Flap Girls School is in it too.
Either way, Natsumi is a common name.
There are also a few idols with the exact same name (when Romanized) although the kanji might be different.
Watanabe Mayu (AKB48 and 3min./palet)
Hashimoto Kanna (Rev from DVL and soon to be ex-Idol Renaissance)
There's also 2 Yokoyama Yuis in AKB48.