Matilda is making her move alongside Serge. Even without her mount and her armor, she's still moving into the front lines. She's used to not having much armor on her, anyway.

Still, support abilities may not be so dampened with all of her current disadvantages. Seeing Corrin ready herself for a direct confrontation with the others, the cavalier readies her magic to prepare a Virtuous Shield for her. It's the least she can do to keep her protected.