I read this series in early-2000s (I'm not sure how old or new it was when I read it at the time), borrowed from the local library. Looking back it was probably just teenager-aimed, but was still really good (well, for an early teenaged-self at the time). Wouldn't mind reading it again, see if it's as good as I remember it... I think it was at least three books long.
I remember several details about the book series, but not more than the details. Still, spelling out the details I remember here, hopefully someone can help me.
Main protaganist is (teenage?) female. During the adventure she got sucked into, she also spends most of the series hiding the fact that she's female.
Travels with two male companions.
Rings of power are involved, each bestowing a specific magical gift when worn. Later in the series, it's found out that each of these rings are actually individual rings from a very powerful chainmail chest-piece. Quest to recover all rings (from possible evil-doing bad-guy?) and add them back to the chainmail chest-piece ensues.
Words of power are also involved. Expends your physical stamina if used, and the magic often takes the form of blue (and spiking?) energy - e.g. a word of binding wraps the opponent up in blue-energy-rope.
Obviously, lots of character development. I think she starts off pretty hesitant and soft-spoken. By the end of the series, and a successful big fight with the baddie, she's quite an incredibly strong fighter, and has developed self-confidence to spare.
End of the series, has to re-integrate into society. The point I think the book ends on is, while struggling to get herself back into the "going back to school regularly" mentality, these mean girls come up to her and mock her for something-or-other. Such pettiness no longer affecting her, but not beyond showing up the girls and letting them know not to mess with her, she easily speaks a quick word of binding/silencing to them, and then walks off smiling/contented, thinking something along the lines of "they'll be fine, especially once the word wears off in an hour or so".
Maybe I'm just daft (it's entirely possible), but even with all these points I remember, I still haven't been able to lock down the exact series by myself... Anyone?