Commission for realtor helping family member

[James Denon]

My girlfriend just got her real estate licence. She is an investor. Since she is new, she cannot become a broker. She needs to be a real estate sales person working for a broker for a while.

If she buys a house for herself or she helps me buy a house, she should keep all or most of the commission instead of giving half or a significant portion of the brokerage firm.

Can this be negotiated upfront with the broker?

What is the common practice for these situations?