For some reason best known to herself - Idioms by The Free Dictionary
for a/some reason/reasons best known to himself, herself, etc. (redirected from for some reason best known to herself)
for (a/some) reason(s) best known to (oneself)
For strange or perplexing reasons that the speaker cannot understand. For reasons best known to herself, Mom refuses to wear her glasses and goes around squinting at everything instead.
for reasons best known to himself (or herself, etc.) used when recounting someone's behaviour to suggest that it is puzzling or perverse. chiefly humorous
for a/some reason/reasons best known to himˈself, herˈself, etc. (humorous) for a reason or reasons which other people find hard to understand: For reasons best known to himself, he wears two pairs of socks.
References in classic literature
Medical men, consulted about her case discovered certain physiological anomalies in it which led them to suspect the woman of feigning dumbness, for some reason best known to herself