Hello and welcome.
I am glad to hear that the doctors are being so cautious and are keeping your wife for observation (and no, they are not being overly cautious). Preeclampsia can move very fast, so don't be surprised if suddenly the doctors will announce that it is time for delivery. Have the doctors diagnosed your wife officially with preeclampsia? The criteria for diagnosis are two BP readings of 140/90 measured twice six hours apart and 300mg or more of protein in a 24 hour urine collection.
Here is also a list of all other symptoms to look out for. Report all of these to the doctors and nurses, so they know what is going on: http://www.preeclampsia.org/signs-and-symptoms
Preeclampsia can move very fast and I assume at this point, they will keep your wife until delivery. Doctors usually will not wait for delivery, especially not beyond 38 weeks with the symptoms your wife is experiencing. They might even consider delivery at 37 weeks.
Please keep us updated as you are able.
MC 3/2009 and 3/2011H
(1/1/2010-1/7/2010) - forever loved and missed; severe PE with Hellp; partial placental abruption, classical c-section at 25.6 weeksM
(Nov. 2012, born at 35.4 weeks) - severe PE
Our pain has been put into words, placed into empty cradles, to remember that all our babies lived, that they mattered and always will. - Field of Cradles http://www.fieldofcradles.org/