YMMV - every woman is going to be a bit different. Some woman can run, and run hard, all the way through and their children have no ill effects. Others are forced to stop at some point during the pregnancy. I knew a 4 time OT qualifier who was forced to stop running for each of her 4 pregnancies - and yet was able to come back and qualify for the trials each time. The fact that she did not train or train hard during the pregnancies did not hold her back. OTOH, some woman who do train have difficulty coming back afterwards because they develop injuries. I was able to run until the day I gave birth to my two oldest, but I could not run comfortably after 30 weeks with my third child. I was able to start running again shortly after birth and had a steady, though not fast, recovery.
My pregnancies were in the 90s, so doctors were just starting to change their recommendations. My own OB called me her "crazy patient" as I continued to run, but she didn't tell me I had to stop - she told me she trusted me to listen to my body. My times were faster than your wife's, and I was 30 with my first. My mileage dropped from 70+ mpw to about 20 over the course of the pregnancy. I only ran at a moderate pace - no speed work once I found out I was pregnant. (Being out of breath and unusually tired were always my first clue of pregnancy). I didn't race, but did do a relay event where I ran 15 miles when I was about 5 months along with the 3rd and it was hard. Of course, that was the pregnancy where I had to stop at 30 weeks.
My advice is for her to listen to her body. If she runs by effort, she can ensure that she isn't running too hard. Naturally, as she gains weight, her times will slow down, and she probably will need to reduce her mileage - but those things will happen naturally.
She should be running to get some exercise and stay fit - not to improve times. As I noted before, hard training during pregnancy does not guarantee a quick recovery, but I think staying fit and healthy does. She doesn't want to injure herself running hard with the extra weight and I'm sure you don't want to injure your child by needlessly depriving him/her of oxygen.
Listening to her body when recovering from pregnancy is important too. While she may have big plans to jump back into racing and training, she will be limited by what her body is capable of doing. Coming back too hard or fast can result in injuries. Note that Paula Radcliffe is experiencing that right now.
Your wife is really young and should bounce back well. As long as she listens to her body and uses common sense, she should be fine. The adjustments to her training will happen pretty naturally.