"I was beginning to think that you didn't need me."
When Fiona said this to Michael, she had said this as a joke. But in prison, she started to seriously believe Michael wouldn't need her at all ever again.
At night Fiona would sit on her prison cot, looking at the bare, white ceiling. It was already bad that, except for meals, Fiona was stuck in her cell. (And even for her meal break, she wanted to stay in the cell to avoid being killed.) For someone who loves running around in high-heeled sandals with shotguns instead of meditating about feeling abandoned, the cell was purgatory.
She thought about the possibility that maybe, just maybe, Michael would move on. He'd forget about her and head straight into work; he'd done it before, several times. He could've done it again. Maybe Michael or Sam or Jesse would find someone else to wire C4 and pick locks on Michael's team. (That is, if his ex Samantha wasn't readily available.) Maybe Michael would fall in love with someone else. Maybe Michael wasn't her soul mate after all.
In that case, Fiona was prepared to die. The sooner, the better. She would have to rip up Madeline's picture of Michael and her Madeline sent for her cell in the mail first. Hopefully Madeline would forgive her after her death.
But, much to Fiona's relief, Michael did come for her. And Michael had gotten her out.
Fiona couldn't wait to sit in the Charger, feel the wind in her hair and crack a joke about Sam. But for the moment, she was where she wanted to be--in Michael's arms. And she never wanted to leave them again.