Lucoa has a dragon form in the manga. It was introduced AFTER the anime was made. KyoAni needed a placeholder Lucoa in dragon form for the opening, which is what you can see on this image.
I personally think they really could've spent a little more time on this placeholder. I wouldn't call it "bad", but it really doesn't fit her at all, and Tohru even says your human form depends on your dragon form and vice-versa. You'd expect a massive dragon who looks serious but not threatening (which is exactly what it is in the manga), not this.