My Mother at Sixty-six
1. With the growing age, the poet’s mother has started losing all her vitality and radiance. The poet uses the simile of ‘late winter’s moon’ for her mother to indicate her approaching death.
Winter, being the last season of the year, is synonymous with lifelessness and dormancy. And, a winter’s moon is also pale-white bearing close resemblance with her mother who, having lost all her strength and beauty, looks ’wan’ and ‘pale’ to the poet. Her mother, too, is in the last phase of her life.
2. The old familiar ache refers to the poet's childhood fear of losing her mother.
3. 'Her' refers to the poet's old aged mother.
4. It is not right to suppress one's feelings every time. It is because suppressing one's feelings a self-destruction button. It ruins mental health. It may also lead to misunderstandings. As it is generally said, "Hearts get broken, by words unspoken."
I hope this helps you.