|Hi Jeff. Sorry to hear about your brush with poison ivy - it's never fun when you're allergic. First off, depending on which source you believe anywhere between 70%-90% of people are allergic to urushiol (that oil in the poison ivy plant vine and leaves that causes us to break out). For those who believe they are not allergic, it's really a matter of time and exposure. The more times you are exposed to urushiol, the more likely it is that you will break out with an allergic rash. Also, the severity will vary from person to person and from time to time. This is a VERY unpredictable allergic reaction. For the first time sufferer, it generally takes longer for the rash to show up - generally in 7 to 10 days. Here's a reference from an MD discussing the generalities of poison ivy and the rash:
Your wife's reaction actually sounds pretty normal (at least for the first few days). The blisters and weeping is the body's reaction to this foreign toxin. We all get this to a certain extent. Prednisone is a common prescription from doctors to treat poison ivy related outbreaks. Prednisone though does have a number of side-effects. Here are some references:
Now I must mention that I AM NOT A DOCTOR. I do bring up these references though as a number of the less common side-effects of prednisone are increased susceptibility to infection as well as skin hives / rashes. Is it possible that your wife is having an allergic reaction to the medication the doctor prescribed? Have you discussed possible treatments and alternatives with him / her? An outbreak this severe is something I've never heard of (again I am not an expert - just someone who collects information like a madwoman about poison ivy). I'd get an expert in or at least a qualified second opinion.
Hope this helps.