Renet is a Timestress, apprenticed to Lord Simultaneous and an ally of the TMNT.
Adventures with the Turtles
Renet appears in the 2003 TV series, along with some minor changes in her backstory. Here Renet is shown to be quite a scatterbrained person who came to her friends with good intentions, but with little practical skill she caused some problems across space and time.
Already in her first appearance, Renet was sentenced to dusting in Lord Simultaneous library because she had accidentally reversed the evolution on a planet of giant worms, and got a six-week penalty. Quickly, she tried to use the Time Scepter to get though her sentence quickly. However, this played into the hands of Savanti Romero, who caused the arrival of the scepter with black magic. Again, Renet befriends the Ninja Turtles, who need to help her with her adventure again and get her out of trouble.
In the 2003 cartoon, the Time Scepter was then stolen by Savanti Romero's pet, which turned out to really be Ultimate Drako- a fusion of the Ultimate Ninja and Drako, both former foes of the Turtles.
Simultaneous later entrusted Renet with the Time Sceptre again, once more dispatching her to defeat Savanti, who now threatened the human race itself. Traveling to the Cretaceous Maastrichtian period with the Turtles, Renet was captured by Romero, who planned to sacrifice her to increase his power. He was defeated by Donatello, and Renet was rescued. However, the Time Scepter fell into a nearby lake and was lost for three months, until Michelangelo found it in the belly of a massive fish he'd caught for the Turtles' dinner. They were then able to escape the imminent asteroid collision. During the adventure, she mentions an adventure she went on with April that hasn't happened yet.
Back to the Sewer
Eventually, however Renet came into the final phase of their training. She made a cameo at the end of the seventh season finale, she used the time scepter - apparently with Simultaneous' permission to observe Casey and April's wedding and noting how it made her cry no matter how many times she been to it, implying she had visited the scene before.