From what I have gathered from my extensive search for information on the internet, I believe, since the F1 visa expired, and she is on OPT she MUST have an offer letter in order to enter US without any problems.... also I heard that if a person stays out of the country continuously for more than 5 months, then the CIS may consider that the person has abandoned his/her status as OPT or F1. In case of F1, the person may be asked to get a new SEVIS I20 and re-enter. If the person has any OPT it gets cancelled.
In case of F1expired/on OPT, then I am not sure how the Immigration officer reacts at the port of entry... I think in your case its best to have an offer letter from a company before reentering and make the stay less than 5months... actually far less than that... reentry may not be guaranteed if you return after 4months and 29 days depending on the then prevailing alert status, (orange, red, yellow whatever) and the mood of the immigration officer... If anybody knows somebody who has gone through this it will help a lot please post your experiences...