If Catherine Doyle was made a ward of state she may be listed, perhaps with her siblings, at Public Records Office of Victoria at Index to Wards Register at North Melbourne. Unfortunately not online but you may find some one who is going there for research.
I'm always cautious, after more than 30 yrs researching, of "family stories". As previously noted, you should always go back from what you know i.e. yourself, parents etc. Catherine herself may have believed her name was Fanning but there is no evidence as yet to support this.
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