#2. To make Becky an even bigger underdog
Becky Lynch is the babyface going into WrestleMania, the clear babyface following Ronda Rousey's sort of heel turn. Booking an injured Becky against Charlotte could be WWE's way of getting more sympathy on her but in my opinion.
Rousey brutalized Becky Lynch at the end of WWE RAW and now she has a truly uphill battle ahead of her at WrestleMania.
#1. Stephanie has special plans for Fastlane
If you notice what Stephanie McMahon told Charlie Caruso shortly after announcing Becky Lynch's suspension being lifted, she mentioned that Lynch would have to sign a Hold Harmless Agreement before her match at Fastlane.
This makes me think that Stephanie McMahon could be orchestrating something for Fastlane. Don't be surprised if Stephanie gets a few members of the women's division together to lay Becky out and 'make sure she can't compete' at WrestleMania.