@SteveH I don't really know enough about your wife's history and PTSD symptoms to offer any detailed advice, but I would say it wouldn't hurt to have an emergency plan in place and to find out ahead of time what medications she can take to calm her down, just in case. (If she's going to be breastfeeding, she's a bit more limited there).
Really, the most important thing is for you not to panic, not to second guess her, and not to hype up any fears about things going wrong. Don't create a self-fulfilling prophecy and be so worried about her having an episode that you trigger one. The most helpful thing for me when I thought I was falling apart in the days after the birth was seeing other people have confidence in me. I was a nervous wreck, I was convinced everything I did was wrong, that I was a bad mother, that I couldn't handle the stress -- you name it. But as soon as I saw someone look at me with confidence in their eyes and tell me a) that this sort of stress and panic is absolutely normal and b) I'm doing absolutely fine -- most of the panic melted away and I grew stronger. That's really the most important thing.
You should also keep in mind that a certain level of stress, anxiety and even depression is completely normal. Especially when sleep deprivation sets in. So she will likely cry a lot and panic, but that doesn't necessarily mean she's having an episode -- that's just a normal reaction to having given birth. Her hormones will be all out of flux for a while.
Personally, i had a few instances of hyperventilating and flat-out sobbing, and I saw a doctor about it but was told that it's actually normal given the sleep deprivation and adjustment period after birth. So don't freak out if you see her crying or acting stressed -- that's something she has to go through. I think it's an inevitable part of birth.
The thing you should watch out for is if she seems to have no attachment to the baby for a sustained period of time, if she takes no interest in it, or if she starts having urges to harm herself or the baby (that right there is PPD or PPP). If THAT happens, doctors will know what to do. But I don't think there's really any way to plan for that apart from being aware of the symptoms and having a doctor on speed dial. Also, that is a worst-case scenario.
Try to go into this with confidence and optimism; leave the worst-case scenarios in the back of your mind and try to focus on the good stuff. I'm not usually a cheery person who promotes optimism, but in this situation, I really think it is extremely important.