IAH will be no problem for a Spanish speaker. All signs and most announcements are in both English and Spanish. The only confusing thing might be changing terminals (which is by train) if she needs to switch from Terminal E (International Arrivals) to Terminal A/B (regional jets).

I would suggest sending her a map of IAH (available on CO.com). She can use this to navigate the airport and point out where she wants to go. IAH has a wheelchair service and a cart service that can help her but I'm not sure about the costs or expected tip.