My mother in law will be retiring soon from her job and we are trying to figure out if she can collect her sick pay. She worked in full time position that was downsized and took another position that was only part time. it now shows on her check stubs that she has inccured 536 hours of sick time. My question is can she collect on this (her employer won't let her use it because she is only part time) ? Also if she does collect it she should ask for the rate of pay she was making when it was earned or what she is currently making. Any suggestions would be great.

California law does not require the payout of accrued sick pay at termination. If she is a union member, the union contract might address this or, if not, company policy. But the law does not require it.

(her employer won't let her use it because she is only part time)

Working part time would not prevent her from using her sick hour, but it would not be paid when she depart from the employer as pattymd indicated.