Legal Question in Business Law in California

No. Co-signing would make you both parties to any contracts, which does not cure her incapacity to contract. There is nothing prohibiting you from starting the company together with you signing for everything. It will just mean that legally it is your MLM company, not hers and you will have to transfer ownership to her when she turns 18.

It would be pretty much up to the other party or parties whether they wanted to enter into such a contract. Some might be reluctant to do so. Also, there is always risk in co-signing for another person.......you can't control what they'll do in all circumstances, e.g., paying the bills when they're due. I'd be inclined to avoid co-signing. Among other things, you'd continue to be responsible for the co-signed contracts even after your daughter's 18th birthday. There is one other possibility for her, however; maybe she could go to court and apply for "emancipation of minor" under Family Code section 7120-7123. I think she would have to be living independently to qualify.