Nowi is a great unit even lacking speed. In normal/hard she has no trouble at all, even if too slow in the beginning and in lunatic she one of the best units, but you have to baby her a little (as you have to baby everyone else but frederick).
Her bases might look terrible, but the dragonstone increases them a lot, and when she joins you, she'll most likely be one of the units with the most def.
And if you are using the wireless features, you can give her the renown speedwing and even buy one dragonstone+ from tiki to make her very broken.