Honey I feel your Pain! I personally have felt the same about myself and my relationship with my kids. I have to admit you are in a much harder situation than I am in, but you are not alone in the way you feel. Let me start by saying maybe the one who needs to see a counselor is you. As a mom, you need to have someone to confide it, someone to trust and talk you through it. Someone who is not going to judge you, but try to help you. I think that's part of what is so great about this website. In a perfect world we would be able to talk with our husbands about everything and they would give us the support we need. But in this day and age, husbands just don't seem to get it. In fact I don't think they've gotten it since the garden of Eden.
The key thing is to sit down your little girl and let her know you love her, that this is not her fault and that Mommy is having a tough time right now. Let her know you're sorry for being mean and that you're trying to be nicer. She's 8, if my 5 year old can get it, I'm sure your 8 year old will too. That was the key to me being able to control my anger isssues. I explained to my daughter why I was mad, but that I didn't mean to get SO MAD. I told her that if I was really mean to her, that AFTER I CALM DOWN she should come talk to me and explain that I hurt her feelings. And what exactly it was that did it. Because WHEN I'M MAD, I'm not aware of everything I say and do. I explained also that this doesn't mean whatever she did wasn't bad, just that it's not nice to hurt people, even if you're the mommy.
After that conversation... I started being more aware when I yelled at her or got so angry I wanted to hurt someone. I started making myself walk away, because I didn't ever want her to pull me aside and say I was being mean. It's been a long tough road and I catch myself A LOT, but it's slowly getting better. And my little girl is starting to realize HOW MUCH I LOVE HER, and that I JUST COULDN'T LIVE WITHOUT HER. Because in all honesty, those little hugs and I love you's really make your long tough day better. And I told her that her hugs can make me happy, so if she sees I'm having a tough day, she should always ask me if I need a hug. And I remember to do the same for her.
Well, I don't know if this helped, but in the very least, know that you are not alone. There are millions of parents with anger issues. And millions of parents who don't understand us. But... as long as you can learn your breaking point... so you don't end up in the paper for losing it and killing your kid... everything can be worked out and fixed. Believe it can be done, give love to your kids as much as you can and smile even when you don't want to. It helps you all heal. God bless you and good luck. YOU ARE a treasure to that Little Girl, don't ever forget it. =)