Slam doubles result at Wimbledon, reaching the quarterfinals with Bethanie Mattek-Sands. Collins struggled outside of the majors though, reaching the quarterfinals at just one tournament (the Charleston Open). In December, she won the Hawaii Open, an exhibition tournament, upon the withdrawal of her finals opponent Angelique Kerber. Collins finished the year ranked world No. 31. At the end of 2019, Collins revealed that she was suffering from rheumatoid arthritis, similar to Caroline Wozniacki. 2020: French Open quarterfinalist Collins began 2020 with three wins over top-15 opponents. She defeated world No. 5 Elina Svitolina in the first round at the Brisbane International before falling to world No. 13, Madison Keys, in straight sets in the quarterfinals. The following week at the Adelaide International, she defeated No. 15 Sofia Kenin in the second round, and then No. 7, Belinda Bencic in the quarterfinals. Collins fell to world No. 1, Ashleigh Barty in three sets in the semifinals. She lost in the second round to Yulia Putintseva at the Australian Open, and dropped outside the top 50 due to failing to defend her semifinalist points. Due to the six-month shutdown of the WTA Tour caused by the COVID-19 pandemic, Collins did not play again after the Australian Open until August. She lost in the opening round of her first two tournaments back, to Jil Teichmann at the Western & Southern Open and Anett Kontaveit at the US Open. However, Collins rebounded at the French Open, where she reached her second career Grand Slam quarterfinal. Along the way, she upset two-time Grand Slam champion and former world No. 1, Garbiñe Muguruza, in the third round (handing the Spaniard her earliest exit from Roland Garros since 2013) as well as 30th seed Ons Jabeur, both in three sets. Her run ultimately came to an end against compatriot and reigning Australian Open champion Sofia Kenin, in a match that for both players was their fourth three-setter of five matches. 2021: Maiden WTA title and first WTA 500 title, return to top 30 Danielle Collins was sidelined for the first half of the season with debilitating pain in her back. She was diagnosed with endometriosis and proceeded to have a "tennis-ball sized" cyst removed. In addition to that surgery, Collins was also taking medication for rheumatoid arthritis. Collins won her first WTA title at the Palermo Ladies Open, defeating Elena-Gabriela Ruse, in straight sets in the final.