I can't seem to find a lot of information on this book/series, but from what I understand, a young girl named Mariko turns into the titular character (see thread title) with a magical wand that she received from Mobile Suit Gundam's Char Aznable.
Also, yes, she pilots a customized mobile suit as Blaster Mari:
http://images.wikia.com/gundam/image...adf5678275.jpg
I've included the first transformation; the rest is just more of the same. If anyone happens to find any more information on this book, please let me know. The premise is too silly to ignore. XD