Ruth, there is actually an avenue all set that can address this. Here in the state of WI you can sign a Buyers Agency Agreement with her (her brokerage) This agreement will have the added benefit for you of having her actually representing your best interest and you can ask her to address the commission she gets on this form. By indicating a higher commission rate on the Buyers Agency Agreement you are actually agreeing to pay the difference at closing. ie - if she (her brokerage) is offered lets say 2% commission by the listing office and you have her put 3% on the Buyers Agency Agreement, you would be accountable for the 1% difference at the close of your purchase. If you think she should have more, this is the perfect avenue.
There will be no worries about what is legal, the IRS and/or licensing issues for her.