on hand

今年も終わりですね。本日の紅白歌合戦にビデオで登場するLady Gagaの元世話係が訴訟を起こしました。ここのon handはどのような意味でしょうか。Lbow-Shoulderくん、お願いします。（ゼミ生 Temple Gaga）
Gaga: Suit from former assistant is 'without merit'

A former member of Lady Gaga's entourage has reportedly filed a lawsuit against the pop star over allegedly unpaid overtime.　According to the New York Post, 41-year-old Long Island resident Jennifer O'Neill was employed as Gaga's personal assistant for 13 months, on hand as the singer conducted her Monster Ball world tour in 2010.　O'Neill is said to have alleged in a lawsuit filed in Manhattan federal court last week that she has about 7,168 hours of unpaid overtime, and is reportedly seeking $380,000 in compensation from Gaga's Mermaid Touring company.　The NYPost also reports that O'Neill claims to have worked for Gaga around the clock without breaks for meals or, sometimes, sleep. She reportedly says she served as the singer's "personal alarm clock," and was asked to perform tasks such as "ensuring the promptness of a towel following a shower."　The paper adds that O'Neill is also seeking unspecified damages in the suit.　Reps for Gaga tell CNN that O'Neill's "lawsuit is completely without merit."
http://marquee.blogs.cnn.com/2011/12/26/gaga-suit-from-former-assistant-is-without-merit/?iref=allsearch