Thanks for all your suggestions.
Can't say I've ever seen a routing between the US West Coast and Budapest that involves either HEL or ARN. AMS is common, however, and KLM often have one of the lower costs.
It appears the EU has some pretty strict guidelines for providing services at airports to PRMs, including having to have assistance provided within 15 minutes of arrival at a request point in the airport even without advance warning.
Considering the seriousness of the stroke my friend had, it's amazing how far they've come, being able to be self-sufficient, including the ability to drive. I'm sure this trip won't be too much of a stretch, but it 's still best to be prepared and take advantage of the services offered as needed.