If you both work, she might not need to consider benefits (health insurance, life insurance), but those can be additional costs. As has been mentioned, taxes are more complicated and expensive. She won’t have paid time off, so she needs to build that into her rate. Depending on how you set it up, she might be able to do a SEP-IRA which lets her put lots of her money away for retirement. Overall, I figured that my rate going 1099 needed to be 1.6x of my W2 rate. That covers retirement, benefits, taxes, and time off. Everyone will be a little different, but that’s a starting point.

Other thoughts:
Companies often lay independent contractors off first.
Setting your own schedule is awesome, depending on how the company you work for handles things
No internal politics is great. No brown nosing at work.
I’ve found not working directly to be awesome. The work just doesn’t stress me out as much. That said, I know it will end at some point and I’ll have to go back to working directly for a company again.