How did the Female Titan cut Eren's titan form?
See page 33, Chapter 32, "Compassion" from the manga.

The previous page followed discussion over Annie as a suspect in being the Female Titan. Mikasa asks Eren, having fought the Female Titan, if anything reminded him of Annie at all. Eren then remembers Annie's stance as a parallel to the Female Titan moving from that same stance into her kick. 

The stance resembles Annie's style demonstrated in Chapter 17: Illusions of Force

The text is spoken by Mikasa to convince Eren that deep down he knows first hand how close to the similarities are.