Using her own lasso on her.

You and Raven lie in wait while Starfire keeps Wonder Girl busy by telling stories of battle. After a while, she is right where you want her.

Or, to be more accurate, it is right where you want it- her lasso!

You summon your energy double and he sneaks over- since his feet make no sound on the ground. He grabs the lasso and tosses it into the air.

Before Wonder Girl can react to this, three words are spoken...

"Azarath Metrion Zinthos!"

Raven takes control of the magic lasso with her powers, tying it tightly around Wonder Girl's torso and extending one end towards Starfire's hand. She grabs it!

"Stop struggling."

The magic compels her to obey.

"What is the meaning of..."
"Don't speak."
"..."
"That's better. You can only speak when spoken to and answer the questions we have to ask," Starfire says, showing her dominant side, "First question- why are you nervous around Tracer?"
"Men have a bad reputation on Themyscera. They once conquered the Amazons. I was trained not to trust them."
"Are you attracted to Tracer, in spite of this?"
"...yes," Wonder Girl says.
"Are you attracted to Raven and myself?"
"Yes."

You go up to Starfire and whisper in her ear. She nods at your suggestion.

"Have you ever had sex with Wonder Woman?"
"Yes, many times. She loves to lick me and I love it too," Wonder Girl admits, blushing a little.

"Do you want to have sex with us?"
"Yes...all 3 of you."
"Do you want us to keep you tied up while we do it?"