You know what's troubling me about Evvie? How she could lay on her back properly? Her tail is more thick and muscular than, say, a cats which could just squeeze a bit to provide room. By common sense her hips would be thrust awkwardly in the air. You could make the argument that her wings would level her out, but they aren't as thick so would have to push outwards at all times. This realization is more bothersome then it should be, let me tell you. 

The only hand wave I can think of is have her wings lock in place to push herself up to match the tail without needing constant force being applied. She could just rest on her side or stomach, of course, but in a battle she'd still get knocked into her back on occasion. and if she's unconscious she'd be stuck that way. If she were to take a powerful hit onto grass then it would just bury in and resolve the issue, so this will likely rarely come up and I'm thinking too much into this.