Elphaba just took what Bonnie said in stride. After all, she knew the other witch was on pain medication and tended to say strange things. Not to mention if she could take Galinda's ramblings in stride, she could quite easily handle Bonnie's. As long as Bonnie's didn't result in a makeover or something. That's where Elphaba would draw the line.
Hearing of Bonnie talk of Elena and Caroline like that couldn't help but make Elphaba feel like she'd missed out on such experiences herself. Her life up until she went to Shiz University had been dark, to put it lightly. She hadn't even gotten her first friend until she was 20 years old. As a result of her upbringing, she was rather socially awkward, but doing these one-on-one things was fine. She looked at Bonnie's wrist as she showed her. "So you three have known each other for a long time? It must have been nice." Elphaba could only imagine what sleepovers were like. Her one duty in life had been to take care of her younger sister, who was ashamed of her and more often than not chastised her for things.
"Okay," she said as she took the bottle and added the proper amount to the water. She handed the bottle back and glanced at Bonnie. "Now close your eyes. I'll let you know when you can open them." It wasn't so much as she was shy about getting naked, it was more she had absolutely no self-esteem and thought she was ugly. She didn't want anyone to see her completely naked, green body when she herself could barely stand to look at it for longer than a few seconds. She grabbed a ponytail holder from by her sink and tied her hair back into a bun so that it wouldn't get wet. She then turned her back to Bonnie, for added insurance that the witch wouldn't see her, at least from the front. She pulled her shirt off and set it aside, then started with her jeans.