This has been brought up in other group reads of S&S, but it's worth repeating that even the name Queen Mab was a rather suggestive one.
Probably the name is taken from a speech from Romeo and Juliet. To take the name from R&J would imply enough, but a look at the speech suggests even more.
In Act I scene iv Mercutio says:
"O, then, I see Queen Mab hath been with you.
... she gallops night by night
through lovers’ brains, and then they dream of love."
The speech starts out with a lot of enchanting fairy imagery, such as "
Her waggon-spokes made of long spinners' legs,
The cover of the wings of grasshoppers,
The traces of the smallest spider's web,
The collars of the moonshine's watery beams...
But, Mercutio's speech turns into something very dark--more like a nightmare--before Romeo cuts him off because he is getting getting carried away. Romeo is very romantic (obviously) and Mercutio is constantly bringing him crashing back down to earth or turning something that was more innocently romantic in intention into something that is full of innuendo (as this speech could be taken).
I think it's no accident that Marianne's reaction to the gift is also described as "a dream of felicity".