#3 For a feud against each other
One of the easiest and most used angles in wrestling history has been the break-up of a team or two friends. There is always an ensuing storyline against each other following a dissolution. It happened with Shawn Michaels and Marty Jannetty and it happened between all three members of The Shield.
Rose has often been the one that has received singles opportunities, like facing Asuka for the SmackDown Women's title at Fastlane earlier this year. Most of the duo's actions have been around Rose telling opponents that they'll never look like her. Deville's role has usually been backing her up. They've also focused on Rose's modeling outside of the ring, like when they were pushing issues of Maxim Australia featuring the Golden Goddess.
Through everything, Deville has been a great friend. She's supported Rose at every turn and even sacrificed opportunities for the sake of their friendship. Maybe that's starting to wear on the relationship like it appeared to do on the latest episode of SmackDown. Deville might be tired of Rose always getting the attention and expecting her (Deville) to be by her side.
In her defense, however, Rose hasn't necessarily treated her friend poorly in a direct fashion. She hasn't been outright manipulative of her friend like Alexa Bliss initially was with Nikki Cross. A feud between the two former friends would be something new for both women and it could even start a move up the card for one or both women.