Actually, sickles are quite blockable, mostly because sickles, despite being small, it would seem sickle users tend to want to keep their opponent as far away as they can, since they can't get the sickle around hips or shoulders if their opponent's in their face. Although, I must admit that someone who's a master with the sickle can most definitely get around any defenses placed by the opponent. 

Also, in Priroda's particular case, the sickle might be the death of her. The sickle, since it's pretty much only capable of cutting skin and [i]maybe[/i] stabbing someone (it is in no way designed to hack, since it's designed to just cut through wheat), depends on a particular mix of grappling with the free hand and pulling down with the sickle once you get it around a shoulder or someone's neck. Unless Priroda's somehow much stronger (physically) than Herriman (I'm dead sure she isn't), she's definitely going to have trouble (if it's even possible for her) with the grappling bit. Also, Herriman definitely has the height advantage, which means if Priroda wants to get her sickle into its "kill spots" (Neck, head, upper shoulders) She'll have to leave herself gravely exposed as she reaches up there.

I'm not saying sickles are bad (because they're really frickin' awesome), but in this particular case, I'm not sure.