Fighting with my sister

Ok so I don't fully want to write this blog because i know what most of the comments will say about praying and apologizing and stuff but I want to get this off my chest.
Tonight I got into a fight with my older sister. I didn't want to and I feel bad about doing it but to some degree she started it (not that it makes it ok) I went into the kitchen to make some popcorn and she was in there. She was heating a tortilla and had put some beans on it, then turned around to use the microwave with it. Anyway my nephew came to the other side of the stove and was trying to grab a bowl off the stove where she had put another tortilla because he wanted it. I thought the bowl had cheese in it and I told him no and he yelled at me, I told him to stop and he yelled again so I smacked him on the butt (he had tried to run from me and I got ahold of him) and he got back onto the chair and was grabbing for the tortilla again so I said "fine have it" and I kinda tossed it toward him across the stove and it fell to the floor. In the meanwhile she turns around and was like "why'd you throw my tortilla on the ground?" I told her I didn't throw it that it had fallen anyway she got all ticked off and I was like "there's more tortilla's over there! I was giving it to him and it fell" she again accused me of throwing it and I said no I tossed it liked this (and showed with a different smaller tortilla, which also fell) and said "it fell just like that" anyway she kept going on about it and I was like "dude it's a fricking tortilla get over it" and she said something else and I forget what happened next exactly but then eventually I told her that maybe if she wouldn't yell at her kids so much they would act better for her. She was like "yeah keep telling me Im a horrible mother like Dad does and so and so does" and I (yelling pretty much the whole time at this point) was like "I never said you were a bad mother, Im' just saying that all you seem to do is yell at them and all this week after work all you did was play on the computer and ignore your kids" which of course she denied and I was like "I'm not the only one who noticed it" So she kept going on about how everyone keeps calling her a bad mother (which nobody ever has but if you criticise anything she says or does she says we are calling her one) so I kept yelling that I wasn't calling her a bad mother! Anyways she ended up saying something like "fine I'll just pack my bags and get out of here" and she went into her room. By now my younger nephew was crying and I apologised to him for yelling and scaring him and I later apologised to my older nephew for yelling and being a bad example. but I did not apologise to her. I couldn't bring myself to do it.
It's hard because even though I would never call her a bad mother it is so hard watching the way she is with my nephews. I feel so bad for them sometimes because she constantly gets mad at them, she doesn't seem to have any patience to deal with them. And she really does come home from work and play games on the computer and talks on her phone and basically ignores them unless she is yelling about something! It's sad. Or if you say something about one needing a diaper change its like "I know I was about to change it, when several minutes later she's still on the computer and if you mention it again she repeats it. Eventually we usually end up doing it ourselves or it takes like 3 mentions for her to get off her own butt and do it!! The baby is only 10 months old and for a long time now he doesn't sleep through the night and even months ago she would be all mad at him when she would be up with him during the night and in a stearn voice telling him "you need to go to sleep, Im tired of this crap! I have to go to work" etc etc!!!! He is an infant for gosh sake!!!! That's what babies do!!! I know she has been through a lot with their loser dad and recently getting divorced and stuff from him but don't take it out on your innocent kids!!! So tonight the things I was saying were true things and I wish I would've approached her about my feelings in a better way (because they've been bottled up ebcause i knew what ehr reactions would be) but I blew my top! So it's hard to apologize for that! I am going to try but in the meanwhile maybe she will finally take an outside look at herself and her attitude and be nicer to her kids! Maybe she will play more with them and give them the attention they want and deserve! Probably not but.... Thanks for letting me vent!