The 33-year-old was found dead in a hotel room in Seville, where she was promoting her autobiography ahead of its release on Monday.
The tragedy comes after De Villota suffered life-changing injuries, including the loss of her right eye, as a result of a crash before the British Grand Prix last year.
"It is horrendous news," Button told Sky Sports News. "Very tragic, the girl has been through so much, more than most people go through in their lives.
"It has been tough for her but this is horrific news and a real shock to the whole paddock and the world of motorsport. We saw her this year in Barcelona.
"We were doing some work for a children's charity and she was the first one to put her hand up to do it. She got a lot of other drivers involved and was doing a lot for the community. It's very, very sad."
A number of Formula 1 teams and drivers have paid tribute to the Spaniard.