Not long after the evening at Winterland, her talent caught the attention of Big Brother & the Holding Company's Sam Andrew. McDonald threw her lot in with the band in 1969, leading to appearances on the albums Can't Go Home Again, How Hard It Is, and Be a Brother. She went on to sing with Mad Dogs & Englishmen for Joe Cocker, and later sang with Leon Russell's Shelter People. Her session work included recordings for such artists as the Rolling Stones, Nils Lofgren, Rita Coolidge, Delaney & Bonnie, and Dave Mason. Her work for other musical artists totals up to appearances on almost 160 albums, more than six dozen of which achieved gold status. In addition, McDonald also launched a solo career in 1974 with the release of the album Insane Asylum. The recording was arranged by Pete Sears, whose formal band associations include Hot Tuna and Jefferson Starship. Insane Asylum featured performances by Tower of Power, the Pointer Sisters, Aynsley Dunbar, John Cippolina, Neil Schon, and Ronnie Montrose. Kathi did not release another solo effort for 20 years, when Save Your Breath appeared. Above and Beyond followed in 1999, featuring contributions from Lee Oskar on harmonica and Brian Auger on keyboards. McDonald devoted more than two decades to recording and performing in collaboration with Long John Baldry, and the duo scored with their version of "You've Lost That Loving Feeling" when it was released in Canada. The song reached number 2 in Australia and also made the US charts