Let's have a laugh : on a less GoogleSearch / Wikipedia / YahooMD / side, general ricin poisoning, if not taken after first 15 minutes, is canon fatal. We don't really know how potent Walt ricin is, we could only assume it's pretty strong since Walt's chemistry expertise has been quite proven among the time. Of course ricin poisoning could be handled right with first response' top notch medecine, which isn't the case with Lydia, since we can assume she got aware of it roughly 12 after ingestion. How about Walt's ricin ? He'd have best interest to powerup his ricin's potency, wouldn't he ? Lydia lives near Houston, TX, which means she'd have hard time calling 911 for ricin poisoning and get an adequate EMT response by then (CDC doesn't deal in isolated cases, they deal pandemia-type stuff and unlike Hollywood told us, they don't have magic wand-like syringes antidotes sitting around).
But let's gofull Hollywood for the lulz: 12 hours after bucco-ingestion, Lydia is in Atlanta's CDC (helicopter, plane, let's not care) : with full pre-diagnosis, there is no way in 2013 we'd know, at a molecular level and without postmortem, what she'd swallow from the last 24h, there is NO microscopic / atomic analysis which would totally nail ricin on a molecular level, especially if Walt made it much more potent. There is no fed genius around, waiting for THAT case. Science, bitch ? No, money. All along.
But heh, we're in Hollywood, let's pretend CSI shit is all around with unlimited budget and we have a fully patent microbiologic analysis within 12 hours (Hollywood time, we're already +24). At that time, unless you're PotUS, VPotUS, CoS or some key cabinet staff / NSC key advisor, there is no way you'll get a proper EMT response. It's all about training and contengencies. You will NEVER get a proper medical response, mostly because ricin diagnosis is easily misinterpreted as food poisoning / behaviour disorder. Good luck telling that underpaid ER doctor you're a ricin poisoning victim, especially if you look like a wornout 40 years old execuctive woman. By textbook you're a strung out employee, welcome to the fucking club. You'll be sent home with chlorazepam and aspirin at best.
TL;DR : Lydia is fucked, deal with it.