The former US Open semi-finalist says she is unsure when she will be returning to the Tour again.
Karolina Pliskova cruised to a straight-sets victory over Tomljanovic in Rome, while Bencic produced a stunning comeback to beat Sevastova.
Daria Kasatkina lost her seventh match of the year to Venus Williams, while Mertens, Sevastova and Collins were also knocked out.
The Austrian has been working behind the scenes with the world No.12 since 2014.
The Latvian grabs her first championship of the season.
Svitolina, Rybarikova and Sevastova all suffered shock losses in the first round, while Pliskova, Radwanska and Venus Williams survived.
Caroline Wozniacki came through a tough test as she beat Anastasija Sevastova 6-2 5-7 6-3 to set up a quarter-final with Anett Kontaveit.
Julia Goerges beat Anastasija Sevastova 7-6 6-3 in a closely-fought match to make it to her fifth WTA Premier final in Charleston.
Former champion Maria Sharapova avenged her fourth round US Open loss to Anastasija Sevastova by overcoming the 14th seed 6-1, 7-6 in the second round of...
16th seed Anastasija Sevastova upsets 2006 US Open champion Maria Sharapova, 5-7, 6-4, 6-2 to reach the US Open quarterfinal for the second year in succession...
World No. 102 delighted the home British crowd as she moved into the third round of Wimbledon with a 6-0, 6-4 win over 18th seed Anastasija...
The WTA has released the finalists for the 2015 WTA Comeback of the Year Award. The criteria to be selected as Comeback of the Year Award...
