Oh , my goodness , I have seen this every where , but to put my finger on it , I will have to think!!

I'm seen some very cute ones at Designs by Sick.
http://www.designsbysick.com/search?firstword=skulls

Not cross bones ans skull, but it might help. If not try embroidery library.

Try urbanthreads.com

There is a very cute one here under downloads about 3/4 of the way down the page.
http://10embroidery.tk/

I downloaded a free one last week from "stickerei".It was listed here in the the freebie section but I only wrote stickerei next to the design .Someone else may have the full link.Size about 90mm X 132 mm in DST format

This is the site killiecrankie mentioned
http://www.stickerei.cc/index.php/other-stuff/free-embroidery-download?start=20

There is a nice one here, skull and roses at EmbLibrary.
http://www.emblibrary.com/EL/search.aspx?search=skull

The coolest skulls are at Urban Threads!

I, too would say Urban Threads.

Five Star Fonts has a collection of girly skulls with big bows... a couple of the designs are applique.
But Urban Threads has a bigger selection that might appeal more to your granddaughter.

I believe one of the talented members on SewForum gave a free cute girly skull and crossbones design.
If you are a member, just do a "search" on the site.
If not a member, join!! The are many, many great free designs and a wealth of info on many topics, especially machine embroidery!
Angel

Thank you to everyone who answered...I really appreciate it....can always count on you cuties to give help.....