J.H.
When my daughter stayed with Grandma the first time I just keep telling her how much fun she was going to have. She loves painting her toe nails and playing with make-up (something mom and dad don't let her do, but Grandma does) so we talked about how Grandma and she would dress up, do their hair and nails, put some lip stick on and "paint the town" which really meant eat some mac 'n cheese with the fancy plates and then watch a new Dora dvd. :)
I just got her excited for her "special big girl overnight"and didn't really focus on mom going but more that she was having a fun and special time to bond with Grandma.
She was fine, she started running off with without a kiss and I had to yell after her "mommy wants a kiss" she was totally fine about the whole thing after I made it fun for her.