Hi Dave
This is the only Olga WILLIAMS I could find, sorry parents are William & Margaret.
1891 Wales Census
Name: Olga Williams
Age: 3
Estimated birth year: abt 1888
Relation: Daughter
Father's Name: William G
Mother's Name: Margaret
Gender: Female
Where born: Llanwnda, Caernarvonshire, Wales
Civil parish: Llanwnda
Ecclesiastical parish: Llanwnda
County/Island: Caernarvonshire
Country: Wales
Registration district: Carnarvon
Sub-registration district: Llandwrog
William G Williams 45
Margaret Williams 36
Olga Williams 3
Thomas Williams 7
Ellen Williams 3/12
Ellen Williams 73
Anne Owens 25
David Jones 43
William H Hughes 19
1901 Wales Census
Name: Alga Williams
Age in 1901: 13
Estimated birth year: abt 1888
Relation: Daughter
Father's Name: William G
Mother's Name: Margaret
Gender: Female
Where born: Llanwnda, Caernarvonshire, Wales
Civil parish: Llanwnda
Ecclesiastical parish: Llanwnda St Gwyndaf
County/Island: Caernarvonshire
Country: Wales
Registration district: Carnarvon
Sub-registration district: Llandwrog
William G Williams 52
Margaret Williams 43
Alga Williams 13
Thomas G Williams 11
Nell Williams 10
John Williams 6
Jane Griffith 24
John Davies 38
Richard Evans 26
This could be her marriage.
Shone Harry Carnarvon 11b 983
Williams Olga Carnarvon 11b 983
cheers
crankypants