[Fluttershy smiles. She doesn't mean to seem that way, and after all it wasn't Mabel's fault that she didn't know.]

M-Mm..probably not...although there...might be versions of you that have visited a different world or two...

[Because that's not going to need an explanation.

While they don't normally have any kind of handshake in Equestria, she understands the concept well enough and offers her hoof to Mabel.]

Mm...it's nice to meet you too...