>>713403023
What it really depends on is which emblem you have to give her. Here are a few sample builds:
>Mage Knight, Lyn (Gentility+/???)
>Mage Knight, Eirika (SPD+/Speedtaker)
>Mage Knight, Byleth (Gentility+/Speedtaker)
The extra slot for Lyn can be anything. Canter? More SPD? Momentum? Anything. If you happen to have no one better for him, MK Citrinne can work with Sigurd since she likes the free BLD boost. It may also be worth considering Sage with Byleth for Thyrsus memes (3-range Elsurge is neato).

>>713418137
Additionally to the Byleth meme, a Sage pulls slightly ahead of MK on the right unit, which is someone with capped BLD and at least +1 SPD cap.