WWE had plans for Natalya to become the Women RAW champion, Rousey Ronda, but those plans were rejected.
The Wrestling Observer newsletter notes that the friendship angle between Rousey and Natalya has been abandoned for weeks, but the plan was always for Natalya to turn to Rousey, at this point in time.
The turn of the heel fell when WWE Legend Jim "The Anvil" Neidhart passed away on August 13. The feeling was that they could not convert Natalya once her father passed, so they went back to Nia Jax for the fight with Rousey.
Rousey is scheduled to defend her title against Jax in the WWE TLC on December 16. Rousey already defeated Jax in the pay-per-view of WWE Money In the Bank.