Perhaps that website had the date wrong?
This website has the date in 1928 and it's the Celtic II:http://www.titanic-titanic.com/big%20four.shtml
Likewise with this website:http://www.theshipslist.com/ships/lines/whitestar.html
So, continuing with the web search, I find the following:http://www.greatoceanliners.net/celtic2.html
It appears she had a collision, but wasn't damaged.
So, my best guess is that it was still operating in 1926.