Generally, it's possible for a L visa holder to petition for a change of status from L1 to H4 while in the United States. Note, however, that the person must document to the USCIS that she is maintaining lawful status in the U.S., meaning she must have recent paystubs for her L1 employment. If the USCIS isn't satisfied with evidence of continued status, they may require that the L1 holder go to her home country to obtain the visa. Further, it's not possible to request premium processing, so this can be a protracted application process. For these reasons, for attempts to change status from L1 to H4 while remaining in the U.S., I would suggest consulting an immigration lawyer about the specifics of your case before deciding how to proceed.