You could call her folk, or pop. I sometimes describe some folk artists' music as "dark folk" and others' as "bright folk" - Rachael Sage is the only one I can think of who combines both, in the same songs. If you know what I mean by that, then you know what I mean by that :)
Rachael's web site is http://www.rachaelsage.com/ and she's got sound samples on it. My favorite album is Smashing the Serene, but to get a sense of her recent work I also recommend the songs Among All of God's Creatures, and Angel (which is about Buffy and Angel :)
The Kendall Cafe is at 233 Cardinal Medeiros Avenue, across the street from One Kendall Square, near the Kendall movie theater and parking garage. They serve food, and have a few tables for people who want dinner, though it's a small place and seats run out. They have three sets a night, at 8pm, 9pm, and 10pm. Rachael Sage will be the third set on Monday night, so theoretically starting at 10pm. I may be meeting geoffroi and a couple of other people there for dinner earlier, and seeing the earlier performers.
The Kendall's web site is http://www.thekendall.com/