If my sister was filing for citizen under her father name but she is 21 years old, will I be able to start over by doing it?

Significantly more information is needed in order to provide a legal analysis of immigration eligibilities, options and strategies for your sister (who is applying to become a naturalized U.S. citizen) and for you (a foreign national who appears to be interested in starting over some type of application). There really is no substitute for you and/or your sister to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options and strategies, and who then could offer legal representation in the often complex application process.