I was born in 1989, so I've been watching this movie my entire life, it's one of my favorites. I guess because I've been watching it for nearly 25 years that I always assumed Nancy Travis was a Brit. I was super surprised to read that she wasn't. As an adult, knowing that she isn't British I am able to pick out the failures in her accent, but for years and years I had no clue.

James Marsters isn't British? Wow, i'd never have guessed. His accent was perfect in Buffy.
But yeah, Nancy Travis wasn't very good at her accent.
"The comfort of the rich depends upon an abundant supply of the poor."

• Voltaire

You are right that her accent could have been better, but some Americans do Brits very well: case in point, James Marsters as Spike in Buffy the Vampire Slayer; Renee Zilwiger in Bridget Jones' Diary; Jennifer Ehle, as Elizabeth Bennett in Pride and prejudice, to name a few. Like anything else, it just depends on the actor.

I am the minority here - I was quite surprised to hear that Nancy Travis was American.
I really believed her accent and I am not deaf or dumb!

Surely they could have hired a British actress to play Sylvia. Was Emma Thompson too busy or something? Same deal with V for Vendetta, Natalie Portman couldn't do a British accent to save her life.

I think the American accent may be easier than the British accent to pull off
awaits angry disagreement from Americans
"What, you don't like rice? Tell me Michael, how could a billion Chinese people be wrong?"

Yep. I don't know why Americans suck at doing British accents, but the British do pretty good American accents. Case in point: Bob Hoskins.

Unless they are deaf, there is no way anyone could have thought her accent was good.
"What, you don't like rice? Tell me Michael, how could a billion Chinese people be wrong?"