Houston has one of the largest percentages/populations of Hispanic/Spanish speaking residents in the US, and I can't imagine that at IAH there will not be many, many folks (likely including CO employees) fluent and willing to help. Certainly, "La Migra" is well equipped with Spanish speakers, although they do seem occasionally officious when it comes to those arriving from Central America.

The advice to provide her with a map is good, and I would go farher to prepare a "cheat sheet" in Spanish to guide her on the way to changing terminals.