Do NOT feel guilty. I reviewed some of your blogs, your SD is a conniving lil B! Yea yea thats not nice to say that about a pwecious skid but I am calling a spade a spade.

You are human, we all have said or done things we shouldnt. What makes us human is we have remorse. I doubt your SD Sybil even has a conscience. 

Go easy on yourself.

Sounds like a normal hard mom morning to me.  I have called my kids brats when they were being one. 

Take a deep breath and have a do over tonight. It is also ok to apologize for snapping at her. But also tell her that you need her to work with you in the mornings so that you can both have a good day!

It's ok to feel frustrated and overwhelmed. We've all been there. I know when the girls (DD & SDs) were younger, I had my moments of frustration!  Once I cooled down, I knew it wasn't my best moment and could have probably handled it better.

She's young so I completely understand how she would take it personal since kids that age have a hard time separating the behavior from the person. Like JMTB said, have a do over tonight. 

it happens and we all have a snapping point.  I have always told my kids..people will snap at times and say things they may not mean.  However, if they do take a look at your behavior..did you have a hand in that situation...if so...then you better adjust yourself before you go after someone else to adjust themselves.  9 times out of 10....my kids figured out...yep they helped create my frustration...(not moving to get their shoes, coats or just plain not moving period...etc) and thus they were partly to blame.  I usually would apologize for snapping at them and then they would conceed they were not exactly being angels either.  I like to think I taught them to look at themselves first and fix what they did before they start casting stones.

You are not a horrible SM. You got caught in the madness of being a SM. It is HARD. Give yourself a break. Start over cuz we all have those days. HUGS

Of course she doesn't like being called names, but you also don't like your morning run amock because she wouldn't get moving. 

You can apologize for calling her a spoiled brat, but you can also make it clear that her behavior isn't acceptable, either:

"SD, I apologize for hurting your feelings. I should not have called you names. That was uncalled for. But, we do need to talk about your behavior. It wasn't fair or right that I called you a name, but it wasn't fair or right to me or your siblings to purposefully miss the bus and not get yourself ready this morning. Our decisions impact people around us. My decision to call you a name hurt your feelings. Your decision to not get ready this morning meant your siblings were cold, your wasted your bus driver's time, and you delayed my schedule for the day. What we do ripples out and impacts other people, and we BOTH have to do better to be mindful of what we say and do and how that impacts others."

You're not a bad mom who deserves to lose her kids. You were a stressed mom who handled a bad situation marginally poorly. She WAS acting like a spoiled brat. She DID cause problems. You didn't lash out because you hate her; you put the appropriate name to how she was behaving. She needs to know name-calling isn't right, but that she isn't a victim who was being picked on by a bully, either.

A few years ago, I lost my shizzit and snapped at SS18. He started crying and ran out of the house to the garage. And I felt like 10 tons of shite. I followed him out there, made a very sincere apology, and promised I would never do such a thing again. That, if there was a problem, we would talk about it. He gave me a rib-cracking hug and thanked me. He told DH (who later told me) how much it meant to him because BioHo had never apologized to him for any of that horrible things she said/did. (FTR, she has never apologized to any of her kids for what she's done. Do any narcs apologize??)

That was a big turning point in our relationship and the last time I lost my temper in front of anyone. It is not always easy to think before I speak, but I try. 

Like JMTB said, apologize to her. Try to work out what both of you can do to make the mornings easier. {{hugs}}

I think calling a kid a spoiled brat is different from calling them stupid or many other names.  Especially if it's true.  My parents referred to me as a spoiled brat more than a few times (probably because I was).  It was a good thing.  It made me think about it, and eventually (never in the moment) it made me want to improve.  Maybe you want to apologize to her for saying it in frustration and anger, but also point out to her what SHE did wrong and what SHE can do to improve.

You should not feel guilty one bit. I find I actually get more upset when DS does something wrong than when SKs do. I suppose because I care more and expect better. 

Both SKs also are rude and will dilly dally to make everyone late or wait for them. Since Thier parents have allowed this and I find this behavior unacceptable. I leave them and make it SOs problem. If I was in your situation. I would have let SK miss the bus then called SO to handle it. They can leave work to drive the kid to school. Then maybe they will actually start to address the problem. 

You getting upset isn't going to change anything if SO allows it.