“You never know how strong you can be until being strong is the only choice you have left.”

Another quote often attributed to her without an original source in her writings, as in The Wit and Wisdom of Eleanor Roosevelt (1996), p. 199. But once again archivists have not been able to find the quote in any of her writings, see the comment from Ralph Keyes in The Quote Verifier above.
A very similar remark was attributed to Nancy Reagan, in The Observer (29 March 1981): "A woman is like a teabag — only in hot water do you realize how strong she is."
Variants:
A woman is like a teabag. You never know how strong she is until she gets into hot water.
A woman is like a tea bag, you can not tell how strong she is until you put her in hot water.
A woman is like a tea bag; you can't tell how strong she is and how much to trust her until you put her in hot water.
Disputed

Source: The Longest Ride

Life and Writings, Young Italy; reported in Hoyt's New Cyclopedia Of Practical Quotations (1922), p. 333

Variant: You can't really be strong until you can see a funny side to things.
Source: One Flew Over the Cuckoo's Nest

Interview with ABC News, as quoted by Hilary Clinton.
2000s

Source: Giovanni's Room

Unmeasured Strength (2011)

Source: Eat, Pray, Love