An L-2 spouse is employment-authorized incident to status and may work for any employer or for herself. She should still obtain the documentation that proves that status for tax and banking purposes.
L-2 spousal work is broad, but the paperwork is hers to keep
Since USCIS recognised L-2 spouses as employment-authorized incident to their status, the spouse of an L-1 transferee does not need a separate work permit to take clients, join a firm or set up on her own once admitted in L-2 status. That authorization follows her status, so it lasts only as long as the L-1 principal's status and her own remain valid, and it ends if the principal changes category. She should keep her admission record and any status documents current so a bank, a client or a state licensing body can see the basis for her work.
Bookkeeping for U.S. clients may involve state-level registration or a tax-preparer credential, which is a professional question separate from immigration. Children admitted as L-2 dependants may study but are not employment-authorized, whatever the parent's arrangements.