I don't think she writes all that much anymore. I remember reading an interview with her a few years ago (unfortunately, I can't find it) in which she said it is harder for her to write these days simply because her life is different. That's not to say that she couldn't produce if she committed to making an album and had to have new songs to record.
I do find it kind of sad that Stevie seems to be in a creative rut right now while her bandmates Lindsey and Christine are having a renaissance of sorts. Lindsey, especially, is writing some amazing stuff these days.
Yes, Stevie just finished up a very successful tour (I credit The Pretenders with helping her fill the arenas, though), but she hasn't produced anything truly new in years.