Lumina works as a huntress. She takes a variety of missions, ranging from simple clean up to high-level extermination. Because she now has a family, she rarely takes long-term missions (anything longer than a weekend). This isn’t so bad because she’s basically a sledgehammer that you swing at whatever you want dead.
Her favourite missions (and the ones that are the most lucrative) are the high-level extermination missions where is assigned an area and told to rid it of Grimm. Her Aura constructs are ideal for this since she can swarm and area with them to kill off all of the little ones and force the bigger and stronger ones out into the open where she can confront them directly. Large companies looking to expand along the frontier are the premier clients in this area.
Money isn’t an issue since Vanille is super rich, but even a single high level extermination mission can make her more money in one weekend than most people can earn in their lifetime. This is because new land (i.e., land that has been reclaimed from the Grimm) must be cleared of Grimm to a certain standard before it can be deemed clear for certain uses (e.g., settlement, etc.). This would normally take several teams of qualified huntsmen and huntresses plus dozens of security personnel up to a month to do. Lumina can do it on her own in a few days because of what her Semblance is capable of. As expensive as hiring her is, large companies can easily afford it, and hiring her is still cheaper than hiring so many other people for so long, many of whom may be injured or even killed depending on the Grimm present.
Now, for safety reasons, Lumina rarely does these missions on her own even if she is strong enough to do so. Instead, she will typically bring along at least a few other huntsmen or huntresses although she will do the bulk of the heavy lifting. It’s actually considered a great way for newly minted huntsmen and huntresses to earn money and learn from a powerful veteran. And that’s not counting the robots and stuff she can bring if she needs them. If she thinks things are going to get really bad, that’s when she gets the band back together.
Other powerful huntsmen and huntresses can make piles of cash doing the same. For instance, the cost of hiring Ragnarok or Saviour to kill absolutely everything in a certain area is astronomical, but you can be sure that nothing at all is going to get out of that area alive. Ruby, for instance, also earns a lot of money on the side doing secure deliveries since it’s basically impossible to intercept her in transit.