She had no conscious knowledge of this (she's in her 50s) until her brother told her in the course of a recent conversation. He remembered her being forced to change hands when she started school.
She now believes this is probably the reason why she's so uncoordinated and clumsy (her own assessment).
Just as a matter of interest, her handwriting is quite neat and legible.
I wonder how many more natural lefties there are who've been forced to change but were too young at the time to carry this memory into adulthood (or have blocked it out of their conscious mind)?