...she feels a wet spot down near her vulva. "Hold on, Diana, Why do I feel wet?", when Diana then responds with "You may or may not have fallen in a puddle."
After hearing her response and contemplating it for a moment, Megan peeks around Diana, seeing if there was any water. Instead of seeing water, however, she sees Diana peeing on her! "Sis, why are you... Why are you peeing on me! And worst of all, why try to hide it!"
Diana starts panicking; She doesn't have anything ready to respond with. Thinking as fast as she can, she responds with "I carried you up here, and I knew I couldn't hold it in long enough to reach the bathroom", hoping Megan buys it. Much to Diana's dismay, however, she doesn't. "Really? And why specifically choose my diaper, when there are spares."
Diana doesn't respond right away, increasing suspicion. However, she still manages to think of something; "I didn't want to risk it, it's a decent walk considering I was about to burst! I didn't want my panties wet!". Megan sees that more as something Diana would do, but is still suspicious of her.