If your friend is a professional and she needs a back up photographer, you're going to have to spend a LOT more money than $1500 to back her up. If she needs an assistant in order to carry her gear, and to help position her reflectors, then I wouldn't worry about it.
The thing about being a professionally paid photographer at any gig is being able to have very fast glass. The camera body doesn't matter as much, though the D90 is a decent start depending on the work being done. The glass in essence SHOULD cost you more than your camera body since it is a lifetime investment, whereas you'll go through several camera bodies in your life.
As for that eBay link. I would stay away from those items. The body is fine, and the 18-55 VR lens is alright for a beginners starter kit lens, but if you're doing professional work it's not going to get you very far if you're working in extreme lighting conditions.
And that Tamron telephoto lens is junk, as is the rest of the crap in that list of items. Most of that stuff is stuff that will just collect dust. Don't bother. If you're going to spend $1500, spend it wisely.
If I were you, I'd look into good used glass, first. A 70-200 2.8 VR Nikor for starters. For portraits, you can save some cash on an 85mm 1.8 at $400 rather than the 1.4 which is more than double the price. Also, Sigma just announced an 85 1.4 at $900 which if it's anything like their 28mm 1.8 or their 50mm 1.8 should kick *** pretty hard, even trumping Nikon's own glass, to be honest. (so long as there are no quality control issues.)
You should state what you'll be photographing, in order to get more help on this subject.
Doug