At the moment I am stumped by Ethel too, I'm afraid. Yes, it's entirely possible she's using a different name in 1901 and/or 1911. Without a birth registration and therefore a birthplace, it's very hard indeed to identify possible candidates.
It's also possible she wasn't English - perhaps Irish or Scottish or from further afield. Are there any family memories of her being from elsewhere?
I'm wondering whether the "nuns' college" clue might help you make progress. Did you have any luck contacting the archivist for the convent? Do you know whether Winifred was of the Catholic faith - I'm wondering whether she might even have been baptised at Sacred Heart?