Look at it this way. She wants to eat healthy and have cereal that will give her the fiber and calories she needs to keep her innards working well. If she eats a big breakfast with you she will likely overeat, not get the type of cereal she likes, and will be uncomfortable for the rest of the day. Is it worth it?
I say let her eat what she likes. You can go out and enjoy breakfast as you wish. Take a laptop or tablet with you and surf the web. WiFi makes every meal taste better.
Maybe this is TMI but since we are anon I will ‘fess up. When I travel, my ideal morning ritual is: Get up, pee, brush teeth, put on yesterday’s shirt and pants and then eat breakfast. I take my time, drink coffee, read the newspaper, use my Kindle Fire, and basically stuff myself. When I finish, I then go back to my room, use the toilet, shower, shave and change into clean clothes. After that I am ready to take on the day.
Maybe she has a similar routine. Let her enjoy the schedule she has perfected over the years. You both will be happier in the long run.