By herself

Also found in: Idioms.
alone; apart; unaccompanied.

See also: Herself

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in classic literature ?
There in that enormous, illuminated theater where the bare-legged Duport, in a tinsel-decorated jacket, jumped about to the music on wet boards, and young girls and old men, and the nearly naked Helene with her proud, calm smile, rapturously cried "bravo!"- there in the presence of that Helene it had all seemed clear and simple; but now, alone by herself, it was incomprehensible.
So Natasha tried to solve what was torturing her by herself.
The singer was snapped celebrating at Proud Camden in London - pouring drinks for herself, eating a cake by herself, dancing by herself, singing Happy Birthday to herself.
"All she did was come out by herself in the ballroom, take a little arabesque and then stand.
After running away to Geneva, Switzerland, with the Brays and spending some time wandering by herself, she returned to England where she began to work in London for John Chapman, a publishing friend of the Brays.
For example, the difference between being an upper-middle-class striver who wears herself out staging a birthday party, and a fundamentalist whose husband moves the whole family into a bus, where she home-schools her five kids all by herself.