The spellings weren't anything that I considered unusual, but I don't really notice 'british' spelling anymore.
Ms. McCaffrey may be a special case, however -- she's originally from Maine (if I recall correctly) and moved to the UK as an adult. She also has a huge readership in the US, and I don't know if she writes separate US and UK versions, per se. I'd guess not, but it's a flat out guess.