The only light rail operating in Washington State is LINK Light Rail, which Sound Transit operates using Siemens Mobility’s S700 model (although some older train sets are still used on the same tracks).
Looking at the Wikipedia page for the S700, you can find these trains all over the US, including California, Arizona, Georgia, North Carolina, Minnesota, Oregon, Texas, and Virginia. They seem to be popular in Europe, too.
[0] https://en.m.wikipedia.org/wiki/Siemens_S700_and_S70
From what I can tell, these train sets are as off-the-shelf as can be reasonably expected, although apparently LINK has ordered their trains to run on 1500 volts as that’s what their catenaries use. Perhaps you’re thinking of BART?
Others have provided good advice about medicinal management. I know from my own personal experience with a close relation.
What I haven’t seen mentioned yet is the FODMAPS diet to control symptoms [0]. This is a diet specifically designed by Monash University, an Australian research institution, to treat IBS and IBD flare ups about one decade ago. It is based from modern science, it is easy to follow (you can run online searches for specific ingredients if you forget), and it allows for quantitative measurements. FODMAPS stands for fermentable oligo-, di-, mono-saccharides and polyols, which are types of carbohydrates that aren’t absorbed well by parts of the GI tract. Another comment mentioned The Specific Carb Diet, but that is outdated and will needlessly restrict your diet and freedom. For example, grains are ok: it’s the soybean oil used in cheap bread that isn’t.
The person I’m close to with Crohn’s enjoys a life unencumbered by their disease. They take their medicine once every two months and they eat out at restaurants or at other people’s homes without a second thought. They eat dairy products, which are not immediately FODMAPS friendly, but avoid garlic, onion, and broccoli. They know they can eat green beans, but not pinto beans. Because of the modern research that underpins FODMAPS, they know they can use garlic oil to get the same flavor but without any of the FODMAP carbs. But, because they follow the diet most of the time, they can occasionally “cheat”, too, and eat some of the high FODMAPS foods every now and then.
You can take charge and your child does not have to suffer. You have agency. Good luck.