What's a reasonable base salary and/or commission rate for executive recruiter assistant?

My sister has been working part time for an executive recruiter that is in her second year of business. My sister helps with research and screening candidates and she’s trying to figure out a fair FT salary and/or commission package. My sister’s been doing this for a year and we live in the Midwest. The candidates are national/international business and legal. Any suggestions on fair compensation would be very helpful. Thank you.