Is it possible to make the connection? Yes! But it really depends on the time of day that here flight from Mexico arrives. Most of the European flights get here between 1:30pm and 4:00pm, so those are the most crowded hours at customs here. Before or after that, it really isn't so bad. Plus, IAH just opened a brand new immigration and customs facility here last month that can handle 4500 people an hour, compared to the facility at Newark that has a capacity of 1500 an hour. On evening return flights from Latin America, I usually wizzed through the whole process in the old facility in about 15-20 minutes, though sometimes as little as 10. The only sticky point is that she will have to recheck her bags after leaving customs, though CO has a counter right there at the exit to expedite this process.