My mother in law just sent me a photo of my son dressed in a dress and with his hair tied up for fun. I am quite upset about it but my friends are telling me it's ok. Do you think it is wrong for her to do that?

I do not think it's inappropriate. You may have a set notion of what your boy should be dressed as or who he should be friends with. But that may not be his wish. Let him enjoy his days and worry about these things when he becomes a teenager. However, if you feel that your MIL has breached your trust or she has done something that you feel is inappropriate, you must convey your feelings to her.