Tin snips will cut it easily. You'll need to cut it off in 2 halves, so should take 4 cuts, 1 top one bottom on both sides. Just be careful as you cut that the other side doesn't move and start to dig in. Maybe wrap her in a towel whilst doing it so she can't kick out. Some breeds you can just wet the foot and the ring will slide right off. Its a 2 person job although I have done it on my own before.
I sold a few of my retired buns as pets the other week, so my while I held the rabbit my OH cut the ring off - took approx 2mins per bun -easy peasy.
The rings are to identify the rabbit so that it can be registered for showing, the alternative is to tattoo int he ears like they do on the continent - I think rings are a bit more humane, but higher maintence. Swings and roundabouts I guess...