Liu, alongside Taylor Fritz, was also given a wildcard for the mixed-doubles draw; they were defeated in the first round by the fourth seeds and eventual champions, Martina Hingis and Leander Paes.

She defeated all three of her opponents in the qualifying tournament, earning her a spot in the singles main draw of a Grand Slam championship for the first time.

[9] In October 2019, Liu won her fourth title on the ITF Circuit at a $25k tournament in Florence, South Carolina.

[19] She reached the third round of a WTA 1000 for the first time at the 2 Miami Open defeating Kateřina Siniaková by retirement[20] and lucky loser Julia Grabher[21] before she lost to 25th seed Martina Trevisan.

[22] At the Italian Open, Liu got the better of wildcard Camilla Rosatello in a first round match that went to three sets,[23] before losing to 32nd seed Marta Kostyuk.

[24] She reached the second round at the French Open thanks to a win over qualifier Ylena In-Albon,[25] but lost to top seed and eventual champion Iga Świątek.

[33] Wins over Irina Fetecău,[34] Storm Hunter,[35] sixth seed Rebeka Masarova[36] and Cristina Bucșa,[37] saw Liu make it through to the final at the Chicago Challenger where she lost to Viktoriya Tomova.

[38] She reached the quarterfinals at the Korea Open, defeating qualifier Ku Yeon-woo[39] and seventh seed Arantxa Rus.

[41] Liu qualified for the Miami Open and defeated Petra Martić,[42] before losing to 10th seed Daria Kasatkina by retiring.

[47] Seven months after her previous match, Liu returned to competitive tennis at the ITF W75 event in Nonthaburi, Thailand, in January, reaching the semifinals before withdrawing due to a neck problem.