I wonder if part of the issue is that she is home with the grandmother, as well? Grandma might not be up to 3 kids in the house, and might not be comfortable with her at your house. Mom might be working. Grandma might very well feel that you are trying to use her as a baby sitter (even though that's obviously not the case!)
My next door neighbors have 4 kids, and DD plays with them all the time--except when their Grandma is over there, in charge. (Usually periods throughout each day when the mom is out running errands, etc) She is in her 70's and I suspect she's just not up to supervising playdates. I know she likes my daughter, etc, but that's about the only time DD isn't welcome to go over there.
My next door neighbors have 4 kids, and DD plays with them all the time--except when their Grandma is over there, in charge. (Usually periods throughout each day when the mom is out running errands, etc) She is in her 70's and I suspect she's just not up to supervising playdates. I know she likes my daughter, etc, but that's about the only time DD isn't welcome to go over there.
