Marni Yang entered the plea at a hearing Wednesday. The 41-year-old woman was indicted last month on nine counts of first-degree murder and three counts of intentional homicide of an unborn child in the 2007 death of 42-year-old Rhoni Reuter at Reuter's apartment.
Prosecutors say Yang was jealous of Reuter's relationship with Gayle.
Gayle and several members of Reuter's family attended the hearing but declined to speak to reporters.
Defense attorney Jeffrey Lerner says Yang maintains she's innocent and is going to "vigorously defend herself."
Yang is being held without bail at the Lake County Jail.