How can I get good indoor maternity photos with a Nikon D80, kit lens, and no extra lighting?

I recently upgraded to a used Nikon D80 with DX AF-S Nikkor 18-55mm lens and I am still learning how to use it. I have really only used it on Auto Mode. Unfortunately, I cannot purchase any more equipment right now or any time soon.

I am supposed to do an indoor maternity shoot in 2 days for a family member and I am really nervous.

Oh. Dear.

Here's the thing. DIFF shoots (doing it for free/family/friends) have the potential to screw up relationships if they go down in flaming disaster. Make sure, if this relationship is important to you, that having the shoot go down in flaming disaster won't hurt it. Set expectations appropriately. Non-photographers always have the expectation that since you got the big "professional" dSLR, that you are now capable of doing professional studio-quality images. But all owning a dSLR makes you is a dSLR owner, not a pro. If you can be upfront and communicate this to them, that is a good thing.

It's not that it's not doable. It's just that it's really really hard to do well, given your current lack of experience and equipment.

I would love to give her studio quality photos. These photos will be taken indoors and will most likely be in a bedroom. Are there any tips someone can give me to get some perfect pictures?

Just me, but I would really really concentrate on this more as fun-family togetherness-time, rather than A Shoot, and to stress that they always have the option to go hire a professional photographer. Treat this as a no-harm/no-foul situation, rather than a "have to deliver" situation. Because perfect is not likely to happen when you're still learning your camera--mistakes are always part of learning.

Most pros can operate their cameras instinctively, because there's so much else you have to think about during a shoot: keeping everybody engaged, happy, and relaxed, your lighting, your composition, your setups, etc. etc. They're used to delivering under pressure to deadline. You probably aren't, and adrenaline and stress can reduce your shooting skillz even further.

Auto mode is gonna suck at this, because it's going to want to shoot off your pop-up flash most of the time if you don't have the camera set right. I'd highly recommend at least shifting to P mode, so you can keep the pop-up flash from firing when you want to. Ideally, you should be familiar enough with your camera that you can shoot in A or M.

She has sent me several ideas and most have a black or white background.

These types of shots typically require lighting gear. The reason the background is black or white is because the background and the subject are lit separately, so that in comparison to the subject, the background is over or underexposed to the point of being white or black. See Zack Arias's white seamless youtube tutorials (Part 1, Part 2). You don't have the gear or experience or room to do this just now, so I would look at these images more for posing ideas and composition rather than "look". If your relative insists on this exact look, then it's time to gently suggest hiring a professional who does have the room, gear, and experience, or maybe doing this for the next baby bump, when you've gotten lighting under your belt.

You cannot do this with just a pop-up flash, because a) it's not powerful enough, b) it's just one light, not two (or three, or four), and c) you can't change where it's positioned in relation to the camera lens [which is why you get that white, flat, deer-in-the-headlights look with it most of the time].

I would suggest making sure that your shoot is in the daytime in a room with a large window. Put a sheet or paper over the window (or use a translucent shade), so that the light from the window is diffused. This will soften the shadows and create a more pleasing, softer look. If the light from the window is super-bright, you might be able to get the background to fade off a bit.

You can also use a big white flat piece of anything (paper, foam core, cardboard, sheet), or possibly, say, a car shade, to reflect/bounce the light from the window onto the other side of her, so that the shadow side is lifted/filled a little. Getting another family member (spouse?) to help you out by holding your reflector might make things feel more collaborative.

I would also bump up the camera ISO settings into the 800-1600 range, at least, because the 18-55 kit lens doesn't open up very wide, and tends to be sharper when stopped into the f/5.6-f/8 range. Ideally, you may want to consider renting or buying a faster lens for portraits. f/2.8 zooms are expensive, so most folks go for primes. The AF-S 35mm f/1.8 DX lens is where a lot of folks start, although the AF-S FX 50mm f/1.8 or 85mm f/1.8 might be good, too.

If you're shooting in JPEG, double-check your white balance before starting. If you're shooting RAW, consider shooting a reference color chart, or grey card (if you have one) before the shot for white balancing help later in post.

Since you use Lightroom, I'd also recommend that, if you have the time and inclination, that you learn how to set up Lightroom to shoot tethered, so that your relative can see what you're getting on the screen as you shoot. I found during my one and only DIFF shoot (I'm typically a landscape photographer, not a portrait shooter) that giving the solemn promise to delete any images my subject finds horrifying can help relax everybody a bit and take some of the pressure off and frees both of you up to try deliberately goofy/silly things. :)

Good luck!