Hello

There is a possible match for your Mary in the UK 1901 Census:
Mary Barrett 4 Born in Swansea Glamorgan Living in Cornwall Illogan
Also found these entries which may be possible siblings?:
William Barrett 3 Swansea Glamorgan Cornwall Illogan
Beatrice Barrett 2 Illogan Cornwall Cornwall Illogan
It may be worth your purchasing credits to find out if the above Mary is yours