Let's first look at the issue of federalism, i.e., the relationship between the federal government and those of the states. As I discussed here, the Supreme Court has dealt with that issue since its earliest days.
In the current debate, federalism is often discussed in the context of the following guarantee given by the Second Amendment:
A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.
The question is whether gun-control laws enacted by state and local governments violate that part of the Bill of Rights, and can therefore be nullified by the courts. I wrote here about a recent Supreme Court decision on that issue.
In this article, Steve Chapman defends Sotomayor's record on Second Amendment jurisprudence. Among other points, he mentions a concept that I plan to discuss more fully in a future post regarding racial issues, i.e., that an appeals court judge is more constrained to follow precedents than is a Supreme Court justice. Chapman argues that, while he and others might not like the results of some of Sotomayor's cases, she has consistently applied existing law in deciding those cases.
Here is a contrary opinion on that question, from Jan LaRue.
One bit of background that I haven't described in much detail: The Bill of Rights was originally construed only to restrain the federal government. For example, no action was taken against some states that maintained official religions, well into the 19th century. It was only after the Civil War, when the 14th Amendment provided for equal protection of all citizens by their states, that the Bill of Rights began to be applied to the states.
The courts have selectively applied constitutional rights to the states, and Second Amendment-based gun rights are one area where that's still up in the air. That's an issue that Sotomayor could well face on the Supreme Court, if the Senate confirms her appointment.