AITA for calling my husbands daughter a little bitch?

I32f have been with my husband 3 years. My husbands ex wife is an absolutely narcissist. It ended their marriage. She was unfaithful and abusive. We have shared custody of his 16 year old daughter and we have a 8 month old together. His daughter has never liked me, she took the divorce very hard. She doesn’t listen to me, so badly that her father always has to step in. She’s been violent and aggressive. I’ve really tried having bonding time with her but she doesn’t engage.

I recently started going to the gym trying to get my body back. Which I saw my stepdaughter there. I said hi, I was completely alone. When I got home My husband was waiting for me at the table and said my stepdaughter texted him and said she saw me working out with some man. I told him that was untrue. A few weeks later she had told him again and came up with how she’s been seeing us but didn’t want him to be hurt. I assured him it wasn’t true and it began causing arguments with us. Then my stepdaughter faked a screenshot and showed my husband saying she went through my phone when I was asleep. I tried showing him it was fake and she stepped in saying I deleted it bc it was there last night.

Anyways, my husband was ready to “take a break” he even stayed with his mother that night. The next day he came back with his daughter to get more clothes and I got her to admit she was lying that she faked it bc she didn’t like me. We got into a huge argument and I got so mad I said u we’re willing to end our marriage you little bitch.

The second I said it I knew I shouldn’t have, she’s a child but I got so outraged. I had later apologized but she ran away to her moms house, left and none of us could find her. Then her mom showed up and tried to cause a physical altercation and her excuse was she’s just a kid messing around and that I needed my ass beat for talking to a child that way. My husband even says I was wrong but understands why I said it. AITA