My 4yo is very disrespectful towards my mom.  The behavior is the worse when I am with them, but it is present all of the time to some degree (my  mom babysits 1-2x/week while I work).  She doesn't treat my father this way at all, and she is somewhat disrespectful towards my husband's parents, but not to the degree that she is to my mom.  By disrespectful, I mean that she outright ignores questions from my mom.  When instructed that she must answer her grandma when spoken to, she screws her face up into a look of disdain, and answers in a very nasty tone of voice.

When pressed for a reason for this behavior, she states "I don't like Grandma".  When asked why, she says "I don't know".  My mom is very gentle, and very hurt by this behavior.  This is her only grandchild.  She pours love and affection on her, although I have encouraged her to taper this off so as not to reward this behavior.

I have tried (and my husband, as well), spankings 'on the spot' at the time of the disrespect, taking away privileges, encouraging good behavior, etc, all to no avail.  She just digs her heels in and seems to have an attitude of 'I don't like Grandma, I don't care what the consequences are, I will not be kind'.

My mom and I just returned from a vacation w/ my daughter.  My daughter refused to go anywhere w/ my mom w/out me, wouldn't let my mom play w/ or touch any of her toys, scowled at her whenever she smiled at her, etc.

My husband and I are very careful to only speak respectfully of our parents, particularly in her presence.

Any advice would be appreciated...