Yeah, I agree that the First legion will likely be headed by their Emperor (Solus)... so that means there could be at least another eleven Legati (maybe even up to 20 of them exist, who knows).

Plus, the survivors of Nael's VIIth legoin may have likely been absorbed by Gaius' XIVth while the Garleans rejuvinate a new seventh legion back at their capital. That is, if they haven't already done so... which makes me join the concensus that our spiffy Elezen female in white could be their new leader.

Either that, or she may just be a top-ranking aide to Gaius.