Shall we file I-130 again as a US citizen because I was told the wait time is less as a US citizen vs US resident green card holder?

Backlogs for visas in each category are reported monthly in the Visa Bulletin issued by the U.S. Department of State. As you can see from the October Visa Bulletin (https://travel.state.gov/content/visas/en/law-and-policy/bulletin/2018/visa-bulletin-for-october-2017.html) there is a significantly longer backlog in the F2 category than in the F1 or Immediate Relative category. When your mother becomes a naturalized citizen there will be no need to file a new Form I-130 Petition for Relative Alien. If your Priority Date already was reached and an I-485 Application for Adjustment of Status already was filed, then at the appropriate time you may notify the USCIS of your mother's new status as a U.S. citizen (and provide a copy of her Naturalization Certificate). Of course, there are many other details that determine eligibility. The naturalization application process often is significantly more complex than it may appear from just carefully reading the form, its instructions and the naturalization statute. Errors made in the application process or failure to provide a full set of supporting documents can create delays or even more harsh consequences. It would be wise for your mother to consult with an immigration attorney about naturalization. After learning all of the relevant information, the attorney could advise about eligibilities, options and strategies for naturalization and then could offer legal representation in the often complex application process.