Three possibilities  (but there may be others).

First guess would be that you notice how rude your daughter is to her grandmother but do not notice how rude she is to you especially when she does not get her own way.

This would mean that her Grandmother probably expects her to behave well even when she is wanting her own way and your daughter does not want you to see that she can behave in a better way.   So your daughter behaves in the way she does when you are there because this is the way she behaves with you - you may have just got used to it and don't notice at home.

Children behaving well with other adults and not with the parents indecates that the problem is more likely to be an interactive one - rather than a behaviour disorder.

Second possibility is that this behaviour might be explained by your daughter believing that to show you she loves her grandmother is some kind of betrayal of you. If this is so it suggests that you may have built up a relationship with your daughter that is too intense and somewhat unhealthy.

The last possibility - less likely - is that her Grandmother does not want to admit how often your daughter behaves badly when you are not there.

Of the three the first is far more likely.

But it is quite possible for aspects of all three to be true at the same time.

Have a look at the FAQ page on the website and give me a ring if you would like some more information about becoming a client.