Collins, who started playing tennis at the age of six, initially embarked on a college career before deciding to turn pro in 2016. She competed for the University of Virginia at the NCAA Division I Tennis Championships in 2014 and 2016 and won the women's individual competition in each case, and in 2015 she reached the quarter-finals.
She gained her first experience on the ITF Women's World Tennis Tour in 2009 and won her first professional title there in 2011. Due to her success as a college player, she received a wildcard in 2014 for the qualification of the WTA tournament in New Haven , in which she failed in the first round, as well as for the main draw of the US Open , where she faced the then world number two Simona Halep only had to give up after three sets and attracted international attention for the first time.
Just a few months after she decided to try it on the professional tour, she won her first title in a tournament in the $ 25,000 category in Stillwater from qualifying and then reached the final at the $ 50,000 tournament in Macon . The following year she was able to win two more tournaments in the $ 25,000 category in five finals on the ITF Tour. She also made her debut in the Wimbledon qualifying tournament . At the beginning of 2018, Collins won the WTA Challenger Series in Newport Beach after a final victory over Sofja Schuk , her biggest title to date, before she then moved into the fourth round of Indian Wells and reached the semi-finals at the American Premier Mandatory tournaments In Miami , where she won her first victory over a player from the top 10 of the tennis world rankings with Venus Williams , she finally achieved her international breakthrough. In Rome she won her first main field game outside of America as a qualifier and was in the main round for the first time at the French Open and Wimbledon , where she failed at the beginning. By moving into the semi-finals in San José , in which she was defeated by Maria Sakkari , she was able to end the year in the top 50 in the world.
In 2019, Collins surprisingly managed to march through to the semifinals at the Australian Open after victories over Angelique Kerber and Anastassija Pawljutschenkowa , where she lost to Petra Kvitová . She then achieved her best world ranking position so far with 23rd place. She also won her opening match at the remaining Grand Slam tournaments and even made it into the third round at Wimbledon . In doubles , she also reached the quarter-finals for the first time alongside her compatriot Bethanie Mattek-Sands . On the WTA tour, she achieved her best result in Charleston by reaching the quarter-finals. Collins was only able to build on her sensational form in Melbourne in Australia at the beginning of 2020 when she made it through to the quarter-finals in Brisbane and the semi- finals in Adelaide , leaving top 10 players like Elina Switolina and Belinda Bencic no chance. At the Australian Open , however, she failed against Julija Putinzewa in the second round and, since she could not defend the points from the previous year, fell back in the world rankings.