Ernie,

if if she has brought you business you would not normally have got then I don’t see why it is out of the question to pay a “finders” or “referral” fee. Since a recommendation is better than an open tender this scenario is often more cost effective to service than paying for speculative advertising. The only fly in the ointment is assigning a value. Clearly 10% of the project value is way out of kilter as this represents a much higher percentage of your profit.

Here in UK we are often asked to provide a “main contractors discount” and/ or accommodate a 12 month retention value on the invoice. TBH in these cases I often just add these amounts to the quote value and look at them as a cost of doing businesss that the client needs to pay for.

MCD is often around the 5% mark.

Effectively in this case she is basically working for you as a commission only sales person. I see no problem with that. You just need to negotiate a mutually workable rate.