Do we as parents create selfish children?

So over the weekend, my daughter did something that threw me for a loop and made me flip my lid. Looking back, it probably wasn't that big of a deal, even in the moment, I felt like I was having an out of body experience...I just HATE that she gets so selfish with her little sister at times. She's 15 and her sister is 3!! I guess a part of it is that she was an only child for 12 years, but she's got lots of cousins and she's NEVER been selfish with them. Then again...it wasn't every day. There's an argument for everything.

My question though, did I do this? Did I give her too much?? Have I enabled her?? I definitely didn't want her to have the life I had. Though it wasn't the worst, it was definitely not the best. I never wanted her to want for anything, and I didn't want her cleaning all the time...now, I can't get her to do anything almost without a huff and a puff and feet stomping, eye rolling...WTH...It pisses me off, but also makes me sad at the same time. I've taken her to shelters during the holidays to serve food, so that she knows this is not the life she HAS to have...Again, we are not the Jones', but maybe we're the Smiths...lol. She just seem so ungrateful...and the selfishness toward her sister even??! Oh, that burns me up!!!