All I really know about Mini Moni is that it was formed by Mari Yaguchi, and was girls who were under 150cm tall. It originally was Mari Yaguchi, Ai Kago, Tsuji Nozomi, & Mika Todd. In 2003 Mari Yaguchi left Mini Moni and was replaced with Ai Takahashi, lifting the under 150cm rule a bit, as Takahashi was 153cm. Mika Todd was replaced Mari Yaguchi as the leader. In May of 2004, Mika graduated to study music in America. Ai Kago & Nozomi Tsuji graduated from Morning Musume, and formed w(double you), and Ai Takahashi remains in Morning Musume.
For the time being. Mini Moni is disbanded.
Currently, Ai Kago is under indefinate suspension for being caught smoking underaged. W's latest single/album releases have been cancelled.
Tsuji Nozomi has possibly been placed in another sub group of Morning Musume, to remind fans that she isn't "Just the other half of W"
Information gathered from various sources, but mostly from
http://wiki.theppn.org/Mini_MoniHope that helped a bit.