*happy dances* I got mom to agree to a pair of earphones, as long as I took a pair as well. The ones we've found and are hoping will help aren't actual true noise cancelling, but they're for phone or gaming use. HOPEFULLY, that will not only dampen just a little of the crowd noise, but it will also make it easier for us to talk in the parks using our phones if we get separated. We're also still taking the foam earplugs.
I don't have a huge noise problem, though there are days when it's an issue, but I have absolutely ZERO problem going around wearing a pair of earphones if it will encourage mom to do so as well. I think this is going to help make aspects of the trip much better.
Thanks so much for y'all's suggestions!!
(By the way, the trick that got her to agree to do it... played her a ride-through video that included the line, in a noisy ride.)