It is blockable only if you were previously blocking the combo that sets it up. Other than that I dont think so. Also keeping your distance from a possible leg grab situation helps alot too. What works for me when facing her is to constantly run and or always have some kind of distance between us.
Yeah, I noticed Sonya's Leg Grab is if you're taking unaware tough to block but I just mash D+block whenever I get knocked down facing a Sonya player to make sure lol.
She does have that one combo right, when it's unblockable after the JL into leg grab, is that right?