Is EVERYBODY wrong in the post ? POST : So it goes like this. 
So for my sisters 2nd child my mum bought them a baby chair swing, RRP $300 paid 150. They used it and then stored it as they weren't sure if they were going to have a 3rd child. I got pregnant with my 1st and they loaned me the chair for use until she grew out of it. My daughter used it and grew out of it and I offered it back to them. I was told that they didn't want to store it as i was probably going to use it for my second (if i had one) so i should just keep it till then. 
In truth my house is bigger and it did make sense. 

So I have just popped it in the corner of my lounge room and after about 6 months it is getting in the way. While my house is bigger than my sisters it is still not big and we certainly don't have a spare room. So at this point I lent it to a friend for her bub telling her that I would need it back for my second. She loves it and it gets some use. 

So this was not an OK thing to do, I think I asked my sister and she said I didn't. Anyway it was made very clear to me that it was not mine to loan as the chair was loaned to me and not gifted. I straight up admitted that I had done the wrong thing, got it back from my friend and apologised many fucking times for my error in judgement. 

So I get pregnant again and the chair is in my possession all so it is all good. Side note my sister is not having a 3rd. So then my sisters SIL (following this?) Gets pregnant 3 months behind me. Fantastic, yay as she is actually lovely but my sister starts asking me for most of the baby items back that she gifted/loaned me. Bearing in mind dear reader none of this stuff I am done with. 
So I was gifted (definitely gifted) a bassinet from my sister that she now wants back. I have actually accidentally broken it and have told her, now she expects a replacement for SIL. It keeps coming up every month or so until my husband buys a 2nd hand bassinet to stop the fighting. Turns out SIL bought her own anyway so we use it for a bit and then sell it on. 

Now the swing which is the current fight, so after my first baby I was told to keep it for my 2nd. So I did. My bub is born and we are using it, then SIL has hers and my sister keeps asking for it back. I keep telling her 'but we are still using it'. Maybe an asshole move but I am a bit pissed off. 
So SIL buys her own and my sister now refuses to take the swing back as no one on her side has any use for it anymore. 
So now sister doesn't want it, but wants me to give her some money for it. Not sell it for her (which is reasonable) but she wants to retroactively sell it to me for what she did have got for it had she just sold it. The suggested amount is $120. The main arguement is that I have had 3 rounds with it including my friend and she, one. 

So my baby has significant, multiple health issues that  have ment that he couldn't sit or roll till well over 9 months so we reeeeaaallly used the swing a lot, and really needed it.. which she was well aware of. 

So AITA?