Have you got any kind of contract on the job or anything in writing or anything like that? If so, there is no way she can legally take your money to pay interest on her loan.

As electrical contractors, we run into this type of scenerio quite often. On our big jobs, our subcontractors know they will only be paid when we get paid. During the construction period this usually isn't a problem because we normally have regular payouts. But when it comes to the final payment - which, by the way, is retainage where the owner withholds 10% of every payment until the very end and then when everything meets with their approval they release the accumulated 10%, which sometimes can run into the 100's of thousands! But anyway, there are more details I could bore you with about this, but the point is this is all done under contract and everyone understands this is the way it's done from the very beginning so there is no question about it. Oh, and material suppliers are paid in full once a month so they are not held to the "when we get paid" process like subcontractors are.

So, if you have some sort of legally binding document, it will be extremely helpful. Also, how and why does she know the salesperson is/was going to share his profits with you? That sounds to me like it should have been confidential information between you two and she shouldn't have known about it in the first place.

Sounds to me like, unfortunately, you are learning about all this the hard way. Being a "contractor," you should always have some sort of written contract, even when dealing with friends. For smaller jobs, we submit proposals that, when signed, are considered contracts so even on small stuff we are legally protected. Probably the best thing you could do is sit down and discuss your feelings with her. Let her know that her business is important to you, but you are not going to put up with her crap. You are probably very important to her business also, so hopefully she will listen to waht you're saying and try to make some changes. In the meantime though, do whatever you can to expand your client base so if/when the day comes, you can just dump her like a hot potato and not look back!