If she's going to try to make it, I would suggest she pay close attention to which booth is going to be taking the flight crews & passengers requiring assistance... and avoid the queue for that booth! It is usually the considered "first" open booth, but that may be the line furthest from where she entered the facility. At least that is the way it works at SEA, it might be different at IAH.

55 minutes is very tight. She can always go online and familiarize herself with the airport:
http://iah.houstonairportsystem.org/international
Although... I am not sure how much help it will be if she is caught up in big lines.

I agree Mexico-IAH-EWR-PDX is a pretty stressful trip. Which would be more taxing though, missing the connection and having to overnight or coming home the long route. (Somehow the thought of all those extra miles actually appeals to me!) Can she take an earlier flight out of Mexico or is there another route from the city in Mexico to??? Perhaps LAX or SFO where she can get a better connection to PDX?

Alison