I don't think its Marek's since her legs aren't paralyzed.  She can move them, but with difficulty.  They seem to weak to hold her or she can't quite get them under her, but no paralysis.  It doesn't look like the photos I've seen of splay leg either?
When I put her in the chick chair, her little legs "vibrate".  She's been able to free herself from the chick chair as well.  She's still eating and drinking and she does try to use those legs but for the most part she's sort of sitting back on her hocks, not getting her feet under her at all.
My camera battery is dead but I'll post pics as soon as I can.