In the title!

To the OP, I would prepare the notes not only for the time on the plane but also for the immigration. Include the instructions for the officer to call a number of the person who is meeting your MIL in case there are any questions. I have used this approach multiple times with my relatives and once actually got a call from the CBP agent at IAH who wanted to know how my cousin managed to fill out the forms in English when he barely spoke a few words. We ended up going through the form over the phone - the officer would read a question to me, I'd translate it and wait for the answer, which I would then translate back into English. It worked like a charm and the officer was great about it. For those wondering, I have sent my cousin a copy of the immigration forms and translation into his native language prior to the trip so he knew what he was doing even without our little dance.