Cosette would be a good doctor because she likes to give everything a thorough examination (I guess that's a testament to her kittenish curiosity)
She'd probably then say, "Hmm, you don't seem to be feeling too good. How about I lay on your chest or shoulder and give you a good snuggle? It's just what the doctor ordered!"
She'd also probably love to be a farmer because she would love the unlimited access to fresh, warm milk (her favorite treat du jour).