[TajadorCombo]

While I wouldn't mind Mei as Espada. I think it'll probably be a just one episode thing. They've been teasing her as Espada since episode 1 but they haven't done it for whatever reason. During their reunion with the Zero-One cast Mei's actress asked Izu's whether she would have liked to transform at some point, I would like to imagine that her agent told her something about it but that wasn't confirmed at the time.

Other thing that keeps her from being a rider is her lack of training, sure Touma didn't have that either but the story shows that his imagination maximizes the power of the Ride Books in a way that fighting skills don't. However, I think they can ask Rintarou to train her, when he eventually becomes allies with Touma again, maybe in a forest or another empty environment in her early stages and then in the black room that they have at the northern base.

In regards of her fighting Sabela, I think either Touma or Rintarou has to take her down, I just feel it would have more emotional impact. On one hand Touma would go against the person framed him as the enemy. On the other hand, Rintarou vs Reika would be a battle between two types of loyalty for SOL, Reika for the institution and Rintarou for its members, his familiy.

Reika vs Mei would be, in my opinion, just girl vs girl, I don't feel those two have enough story together to create an exciting battle.