I can identify with you because there are members of my family who act like that. They are passive aggressive and try to take things out on me...I finally learned to let them be that way to their hearts content, BUT I do not allow them to make me feel bad.
They want you to feel guilty, as if you have done something to them...(that makes it their problem). I would turn it around on them. Tell the cousin thanks but no thanks. If she wants to give the gift to your daughter fine, if not, that is fine also, but you will not be treated like that by her ever again.
I would tell your mom the truth. One of the reasons you don't come over more often is because of the way she tries to guilt you out and control you with it. You don't need that in your life, and if she wants you to come over more often, then she needs to be respectful.
I think if you do that it will make them sit up and take notice that if you aren't treated with respect they won't see you very often, and you certainly won't be controlled by their passive aggressiveness...anyway, that is just my two cents worth:-)
Have a Happy Birthday:-)