Nico Rosberg's shock decision to retire suddenly upset Williams' plans. Its driver pairing was signed and sealed, but Mercedes' will to hire Bottas turned everything on its head.
"Pretty soon after Nico's decision, I had Toto on the phone," Williams explained at the SPOBIS sports business congress in Dusseldorf, according to Speed Week.
"At that point we had agreements with Valtteri and Lance Stroll - everything was done, everything was clear. The new scenario after Nico's decision put us all in a difficult position.
"When it comes to future world champions, the name Bottas has been mentioned regularly in recent years. I am anxious to see how he goes.
"Valtteri has grown close to our hearts over the years - I just wish we could have given him a better car. But I'm happy he will get that chance at Mercedes."
Filling Bottas' big shoes was difficult enough, but a prerequisite linked to title sponsor Martini added another problem. The famous alcohol brand demanded that at least one Williams driver be at least 25-years-old.
"The problem is that most of the available drivers in Formula 1 were not 25. So it meant six hectic weeks for us," she added, referring to the negotiations that eventually brought Felipe Massa back to the team he had left just a month earlier.
"It was not boring. Actually this is always the case after the season, because the preparations for the following season have already started. But this time, everything was a little different."