Nanny to Casey Johnson's Estate: Pay Up, Kiddo

Casey Johnson's estate may have to tap into its limited funds -- because a woman who claims to be her former nanny has filed a nearly $12,000 creditor's claim against the estate.

According to documents filed Tuesday in L.A. County Superior Court, Tatyana Gurskaya claims she was hired to watch over Casey's daughter Ava back in August 2009 ... but was never paid for her services.

Gurskaya claims she's actually owed $1,250 -- but is tacking on nearly $10,000 in penalties and expenses ... for a grand total of $11,820.

As TMZ first reported, a rehab facility in Malibu filed a claim against the estate for $74,750 ... and Casey's estate was only valued at around $75,000.