A couple things to ask first:
1) How many weeks pregnant is she?
2) Is this her first pregnancy?
3) Have you read through About Preeclampsia in the main section of the website? I would recommend it.
And a couple bits of advice:
1) Take her BP sitting up every morning about ten minutes after she gets up.
2) Write it down
3) 140/90 qualifies as high blood pressure. It is potentially a problem because it can cause lots of complications. It is good your wife's doctor is asking you to monitor the BP.
4) I would ask the doctor to discuss preeclampsia with you. Does he think she has it? What plans does he have? Some doctors will put her on antihypertensives. Depending on how far along she is--others will deliver her. You will need to ask him what his plan is and ask what YOUR options are. You should know if anything--doctors do not tend to deliver babies early unless they feel the risk to the mother outweighs the benefits to the baby of staying inside. Also, this disease can be dangerous to the baby--so if they say it is time to deliver--usually--they are saying this because they feel there is no other choice.
Please let us know how you and she are doing. I know this can be scary. We would be happy to help you understand what is going on.