I agree with Doubledown.
This is a generalisation and may not apply to your wife, but some people who are artistic may not be time or income pressured - that is she may have a different personality, that is not so driven, or organised, or stronger with regard to creativity i.e. ideas and creative possibilities and less strong in actually doing. There is also a difference between creating work that is saleable and creating a product for sale in a time contingent fashion. If she creates a business that grows, and she makes the items that sell, in some sense she will need to forsake her creativity and "churn it out" to get volume. Like wise she may have to produce what is "hot" and in demand, when she'd rather be creating something different.
I think it might be time for a sit down and gentle exploration of what the issues are. Does she keep talking about making it a business because she feels she should be producing income?, or, are there, as Double down suggests, some real issues with things that are not her strength. If you have complementary skills you may be able to assist. If she is on board with financial goals that require her to contribute income, another option is to get a different part-time job to make so much $ and keep the artistic stuff as a side.
I don't know anything about how your family works, so this is just another stab in the dark, but what is the division of house-hold labour? Once the kids are in school there is more spare time, agreed, but the number of free hours may not be as high as it seems, depending on the number of hours they are away and how they get to and from school. (eg mine used to be away 6 hours, but required dropping off and picking up which reduced the "free time" by another 30mins.) Those 5 or 6 hours fly by if the rest of the household is not contributing much to the daily chores. Its not reasonable to expect her to work up to 5x6 hours= 30hours a week in paid work, unless there is a strategy for how all the household chores are going to get done. If you have been a one parent working home, there will need to be readjustment/reallocation/ change in expectation, to get the second parent free to do paid work. If she is doing the artistic work at home, there will need to be agreement that once the kids leave the house, she does NO more chores, just does artistic work for the agreed hours. They will come home and find the house is still a mess like they left it and mom hasn't made cookies for afternoon tea. Mom will then be busy doing chores and dinner rather than doting on them. Depending on her feelings on the matter, this might be hard for her also ie its a skill to make boundaries to work at home, if you have been the main homemaker.