Hi Philip
I found a couple of birth records for a Mary Williams in Tralee that would suit but amn't sure which one is yours. If you have a death cert for her, the age on it might help narrow it down. Also by looking at the names of Mary and Robert children will give you a good idea. The writing on some of these parish records is barely legible so some of the names below are likely incorrect, eg. Gobineta. Again, looking at children's names will help you piece it together.
First Name-Mary
Last Name- Williams
Baptism date- 14 Jan 1793
Parish- Tralee
Diocese- Kerry
Fathers Name- John Williams
Mother's Name- Ellen Mahoney
First Name- Mary
Last Name- Williams
Baptism Date- 27 March 1826
Parish- Tralee
Diocese- Kerry
County- Kerry
Fathers Name- Gulielmi Williams
Mother's Name- Anne Ohilichan
First Name- Mary
Last Name- Williams
Baptism Date- 29 Sep 1826
Parish- Tralee
Diocese- Kerry
County- Kerry
Father's Name- Richard Williams
Mother's Name- Honora Ollonie
First Name- Mary
Last Name- Williams
Baptism Date- 26 Feb 1829
Parish- Tralee
Diocese- Kerry
County- Kerry
Father's Name- Richard Williams
Mother's Name- Gobineta Williams