Is it possible for her to come in on the same tourist visa and submit the I-130 and N-400 simultaneously?

Use of a visitor's visa is exclusively for foreign nations who intend to enter the U.S. for the purpose of a visit and who intend to return abroad. If a foreign national were to enter the U.S. with a visitor's visa, then promptly marry and file an adjustment of status case (not a N-400 Petition for Naturalization, which is available only after expiration of a statutory period following becoming a Permanent Resident), the USCIS may view that as constituting fraud, with very harsh immigration-related consequences. It would be wise for you and your fiance to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options and strategies to attain your goals, and who then could offer legal representation in the often complex application process.