The 26-year-old died on Friday, November 26 and the governing body and her club Stirling County made the news public on Tuesday night.
The back-row started all three of the Scots’ Six Nations games earlier this year at No 8 and was part of the squad that travelled to Italy in September for the European leg of the World Cup qualifiers.
There she came off the bench in the win over Spain in the 66th minute to earn her 19th cap for her country. She was not involved in the recent November Test win over Japan.
Cattigan made her international debut against Wales during the 2018 Six Nations and her passion for rugby had begun at the age of five when she joined McLaren Minis, which were based in her hometown of Callander.
She previously cited that Scotland’s historic win against Ireland in 2018 was one of her personal highlights, with the side claiming an away victory for the first time in 12 years.
A Scottish Rugby statement said: “The thoughts of all our people and players go out to Siobhan’s family and many team mates at Stirling County and Scotland at this incredibly difficult time.
“Specialist Scottish Rugby employees are now providing on-going support to those most closely affected.”
A Stirling County statement said: ‘Shibby’ was a team mate and friend and we deeply mourn her loss. Our love, thoughts and heartfelt condolences are with Shibby’s family at this devastating time.
“We very much hope their privacy will be respected by everyone as they deal with their tragic loss.”