Sister's Buttplug Complications

My sister suddenly ran into my room and closed the door as quickly and quietly as possible. She wasn't wearing a bra under her shirt, her pants were hastily pulled up and she had a panicked expression on her face.
„I need your help.“, she said.
„What happened? Are you okay?“, I asked, starting to panic as well.
„I- well... this is a bit embarrassing but you're the only person that I trust enough to keep this a secret.“, she replied.
„What is it? What did you do, you're not hurt, are you?“, I asked, still fearing, that something serious happened.
Nervously, my sister explained:“ I may or may not have bought a buttplug recently and it may or may not be stuck and I can't get it out...“
I was speechless. I knew my sister did kinky stuff, I caught her with her now ex-boyfriend on a playground swing once, but I didn't know that she had any toys. She must have bought a bunch since she turned 18 recently.
She began getting nervous again, because I wasn't saying anything, so she continued:“ I really don't want mom and dad to know that I have this, my friends will tell everyone and I don't want to have to call an ambulance. Please! Just help me, I'll do whatever you want!“
„Don't worry, I won't leave you to suffer sis. I just had to process this situation for a moment.“, I replied. „So how do you want me to help you?“
„Well, it really hurts when I pull on it and I can't get myself to just pull it out.“, she said.
„Alright then.“,I said, sighed and gestured her to turn around. She pulled down her pants and turned her butt towards me. She wasn't wearing panties either. She must have been naked and just put on a shirt and jeans to come to my room. I kneeled down. Her pussy was still wet and the buttplug deep in her ass. I tugged on it lightly. My sister moaned and silently apologized. I just laughed and continued to try and carefully pull it out. I grabbed her ass with my left hand and pulled on the buttplug with my right. It wasn't enough.
„Did you not use enough lube?“ I asked.
„I got too excited and just used my- uh...you know...my juice...?“, she replied.
„Oh, I see, bad idea, use lube next time.“, I said.
„Maybe if I...“, I thought out loud and spat on my Sisters' asshole.
„What the fuck are you doing?“, she said, outraged.
„Relax, Im trying to lubricate it to get it out of there.“, I calmed her down.
After a while of trying, I finally got it out, with a fairly loud *plop* noise and a moan from my sister. The buttplug was a lot bigger than I thought and so was her asshole because of it.
„Thank you so much!“, she said, ecstatic. „I owe you one now.“
„Yeah.“, I said.
„Literally anything.“
„Gotcha.“
„I'll even suck your dick“
„Okay?“
„Or let you fuck my stretched asshole.“
„Did you do this just so I would fuck you?“
„Possibly...“
„Get lost, I'm busy.“
Frowning, my sister left the room, turning back with a hopeful look on her face and her stretched anus pointing towards me. I simply pointed to the door and she turned and left.