Her eyes seem to be always watching OMT to see if she has done or said something wrong!
I don't think she's worried for herself. She's lived with OMT for what, 40 years?
I think she worried about what OMT might try to do to Ennis or what Ennis might do to him if they got into it.
If you look real close at the expression on her face when she says "You come back and see us again."
(It's right after OMT has said the ashes are going in the family plot) It's almost as if she's telling Ennis she'll have something more for him when he does (maybe the ashes?)