You run your own law firm, I think you'll be alright...

just get her a job as the janitor

Well the firm's customers could benefit and the hair dresser could be an alibi! Or maybe that's just legally blonde!

Have her work the mail room.

She could maybe be the receptionist or file papers in the back

OP, she's family. Don't take too much tension in deciding what to do. Give her a job where she can easily learn the skills necessary [i.e. secretary/assistant, courier, housekeeper]. You never know what blessings will come your way later. Set the ground rules and expectations. Even though she's family, it's business and professionalism is key. If she doesn't adhere to your rules, explain to her why she must be terminated. Who knows? Perhaps one day she'll either go out looking for her own line of work back in cosmetology or she just may excel in your field and you just may inspire her to go back to school and get a degree in law. Keep your chin up and smile on.

You own your own law firm - you must be doing well and not need dad's money unless he's got millions - so in this case think of the three words invented for just such an time... **** YOU DAD!

Sounds really useful, if you get any good cases at least your hair and your clients hair will look nice. That is unless the reason for your sister to be looking work is that she's terrible with hair. Although the fact that she chose that path and was able to receive a degree of some sort in cosmetology suggests she at least knows a thing or two. At least giving a good opinion on styles to help present a good image when standing before a judge in any court of law. Appearance is half the fight.

Disownment might not be a bad option

Make her the secretary