She said: "I am quite concerned that the trains will go 140mph. It takes more than a minute to stop if you are going 125mph. How long will it take at 140mph?"
Answer: More than a minute, and a little bit longer.
I recently returned home at around 530 mph (relative ground speed) with little by way of ill effects beyond the usual slight bloating, similar to what happens to a packet of crisps at altitude. That is best dealt with by leaving the aircraft by the rear steps. With the APU running, no-one will hear. Be careful, though, not to confuse this with post-curry syndrome. You still have immigration to clear.