Why does Rosa expect Rydia to be able to easily handle Black Magic?

[*Laurelindo*]

Or that these magic creatures that are being summoned are rooted in the elements. If you think about it most summons are elemental based creatures.

Well, that's true.
Actually I always kind of viewed Summons as some type of "higher form of Black Magic", and saying that they are rooted in the elements would make sense.
Of course, there are a few specials like Golem and Carbunkle, but theoretically those creatures can also be rooted in certain elements.

Don't have one, because I'm not reading too much into it .

It isn't dangerous to present random theories about what you might have thought about it, though;
you now, just for the sake of chatting about it for fun.
But you don't have to if you absolutely don't want to.