A heel turn doesn't make sense because it's pretty much the same character. There's also no need for a conclusive finish to Becky/Shayna at WM. Book the match in a way where they can continue the feud. Last night was probably the best match Becky's had that was a straight one on one match. The counters between Asuka were crisp and well done. Shayna can do the same thing with her. If they feel compelled to have Becky retain at WM she should win by countering Shayna's submission into a pin. Shayna can go up the ramp and tell Becky she almost had her.