EXCLUSIVE

Save Ferris singer Monique Powell isn't backing down from a nasty lawsuit filed by her ex-bandmates -- in which they accuse her of hijacking the Save Ferris name for her own personal use -- in fact, she's going full offensive ... insisting the band belongs to her now.

As we reported, the former members of Save Ferris sued Powell over a "Save Ferris" reunion show she had been promoting this summer -- claiming they had approved no such show, and she had no right to use the Save Ferris name after the group disbanded in 2002.

But Powell just filed a response, insisting the group never disbanded ... the other members just chose to leave ... meaning she's the last member standing. As a result, Powell argues she's the sole owner of the band's name, and can do with it whatever she likes.

Powell also thinks it's BS for the ex-members to claim they own the name when they haven't used it once since 2003.