Aquamarine, can you see that by calling your DIL the gate keeper, you are basically saying your son is incapable of making his own choices or making a choice to contact you? Think about how that sounds to your son. I once said to my husband, when my MIL said something similar, "You realise your mother is suggesting you are spineless?" Men are very capable of making their own decisions about relationships and trying to sort out difficulties, if they choose to. For my husband though, he chose the comfort of just withdrawing rather than saying to his mother, "Hey Mum, there's a problem here, can we talk about it?"
If women are forced into the role of social secretary, then I suppose they are reasonably the gate keeper of their households, especially if the husband decides to put that on her too.