Keoni,
One of the best ways to learn about
Lupus is to read on the website
www.lupus.org. There you will see the 11 main symptoms that generally indicate Lupus.
One of the main things to know is that GP's/PCP's generally run an ANA test before deciding if something is indicative of Lupus or not. Then, and only then, they will refer to a rheumotologist - the rheumotologist is the Dr fully trained and experienced with Lupus and many other auto-immune diseases. The "hidden trap" in this is that ANA is NOT a firm indicator of yes/no for Lupus. If your niece is showing 4 or more of the listed symptoms, your sister will want to take her to a rheumotologist regardless of what the GP/PCP is advising (and regardless of the ANA results).
A good way to find a rheumy who is "good at" Lupus is to visit the Lupus website above, find your local chapter, then ask what Drs are active on their advisory board -- these are the Drs most interesting in helping Lupus (and other auto-immune) patients.
Let us know how it goes.
PS. This website is neither pro or con on various treatments -- treatment advice is solely that of the individual.