I think all you can do is look at what you gain by being friends with her, and what you risk to lose (or gain) by no longer being friends with her. Do you socialize with her offline at all any more, or is it just Facebook? Are the funny cat pictures worth the discomfort of her political views?

The other option is removing her from your news feed and only checking on her occasionally or when you have something specific to share with her. It's a little bit of a cop out, but it might also be a good compromise?

(Says the one who put her father on her blocked list so he can't see anything she posts....)