Quick background, I'm livid and waiting for DH to come home to discuss how to approach his mum. DDs are 10 and in laws have been collecting them from school two or three times a week for years.
MIL is a complicated person but I have always trusted her with the girls and thought they had a close loving relationship until recently. I have noticed that she has a soft spot for DT1, thinks she can do no wrong and is harsher with DT2 and I have mentiond this to DH on several ocasions over the last few months but he thinks I'm over sensitive about it all. A friend of mine also commented on her different attitude to the DD's.
Anyway, this morning DT1 said that yesterday after school she and her sister had been playing around with a teddy, grabbing it off each other and running off up the garden, and DT2 had taken it a bit far and refused to give it back causing a row. MIL then said to DT1 'I hate that girl sometimes'. DT1 said she was shocked and said to her nana 'You can't really mean that nana' and she replied 'Yes I do'. 
So what now, I haven't rung MIL even though I really want to, but think DH should deal as it is his mother. DT2 heard the comment and told me it had upset her but she has heard her say it before
. She has low self confidence as it is and is having a hard time at school at the moment with friends, as well as her body changing etc and I could sit here and cry at the thought of her hearing her nana say that to her.