My best advice?

Tell your friend to work in the food business for a minimum of two years before trying to start or run a business there. And your friend should work in a place as similar as possible to what she's planning to do. For example, if she's planning on operating a Mexican food truck, she ought to find a job with a food truck, not an upscale bricks-and-mortar restaurant.

From your question, it appears your friend doesn't even know whether he/she wants to operate a food truck, a small restaurant, or offer online catering. That's a guaranteed recipe for disaster.

Tell you what. Tell him/her to get a job in a small restaurant. If that doesn't work out well, then your friend should work in a food truck operation. I definitely would advise starting out with online catering. (There's no low-risk way to get the experience that's necessary.)