Ninian question

Once again i've been pity broken while summoning for Summer Cordelia. First time it was a +Spd -HP Linde, welcomed since i never summoned her. This time it was from a Ninian +Res -HP. I already have a +Spd -HP Ninian that i summoned when she first came out and she's doing quite a good job as a dancer and dragon unit. Now, the struggle is what to do with the new Ninian. I mean, i could merge them but it doesn't seem like that good even if my +Spd one will reach 37 Spd. And also i don't think i would need to inherit Fortify Dragons to another Dragon unit since i can use Kana (M) for that. What do you guys say?