I don't think of SMG as an indie actress at all. She tried, very hard, to become a big movie star after Buffy ended and she's tailed off in recent years. I mean, The Grudge, the Scoobie-Do series, Scream 2, even ones when she was younger like I know what you did last summer and Cruel Intentions, all of those were major Hollywood productions.
And I mean, Ringer? That was a CW soap opera really, hardly an indie show.
And, I think SMG got kind of typecast, which is a shame. That's happened to plenty of other actors (although to much greater extents) and they took what they could get. I mean, Mark Hamill didn't just vanish from the acting scene post-Star Wars because he wanted to. It was because no one could see him as anything but Luke Skywalker. I think that happened, to a lesser extent, to Sarah as well. Hell, it's happening now with Tom Welling.
Sure, she's had roles in smaller budget films (which is what I think most people think of when they think of an "indie" production) but so have many actors and actresses who have been in huge movies. All those movies, Buffy and Ringer don't really fit that mold.