The British team switches to Mercedes engines from Renault for the 2014 Formula 1 season, but Williams has already had a taste of what the partnership will be like as work has progressed on its new car in the later stages of this year.
When asked if the first few months of working with Mercedes had surpassed expectations, Williams told AUTOSPORT: "Yes, I think it has exceeded them.
"That's great because our expectations were at a very high level anyway, which is why we chose them.
"You know how professional that operation is, and everything we have seen since we signed that contract hasn't changed our mind."
Williams added that having the Mercedes F1 engine programme based in Brixworth in the UK is also a benefit compared to working with Renault in France.
"The easiest thing for us in the whole thing is that they are just down the road, which makes it easier when you are trying to work with them," she said.
"Going over to France is a long trip and not necessarily conducive.
"But our engineers can dash to Mercedes countless times and they come to us. We are really pleased."
Williams said the team is optimistic about how the Mercedes engine will stack up compared to the Renault and Ferrari units, but she admitted that it is impossible to tell who is going to have the advantage next season.
"We are [excited], but I don't know if anyone really knows where they are with the engines and I don't think we will know until the first test," she said.
"But it is going to be fascinating to see where each engine is, and I hope the Mercedes is clearly the best in the paddock because it will help us move forward."
WILLIAMS ENGINE SUPPLIERS 1977-2013