Get your child out of that situation ASAP. No way I would make my son feel in danger in his own home. 

What did your DH have to say about any of this??

Get nanny cams. This child is hurting your baby, Id step up the momma bear act and tell SD in no uncertain terms that she is not to lay a hand on your child ever again or there will be dire results. Let her use her imagination as to what that means.

Tell your partner SD is to not ever be alone with your child. This is disgusting behavior.

I don't care how old your SD is....giving a 2 year old a black eye and making her bleed is abuse and if CPS were called in, they'd remove your baby from the home. Your child is in DANGER. Don't play with this. I personally know someone who's baby was attacked by a friend's 6 year old and that attack left the child permanently disabled. Your SD needs to be forcefully told that she will NEVER lay a hand on your 2 year old again. And your DH needs to be a damn father and parent HIS kid. Sending her to her bedroom is NOT appropriate punishment for what she did. 

I'd be a screaming wild woman if someone did this to my baby and I'd put both SD and DH on notice. SMH

I'd invest in cameras ASAP to show DH the proof in the pudding.

Also my experience with men has been they don't really give AF until it affects them. I'd totally disengage with the feral little one until he addresses behaviours. I'm a full time mom to my SD8 but my DH's 4yr old twins? I'm totally disengaged until he addresses their shit behaviour. It can be done.

1. cameras w/ or w/out Dh's imput. 

2. child is to be w/ her dad or not in the house w/ the little one

3. if anything of any form happens again, DAd has to make arrangements to stay elsewhere when he has his eldest. no excuses, no exemptions. 

4. stepchild gets informed of this now. as does s's other parent. this is the begining of a road that her parents need to focus on. 

5 - infinity ... WTFudgsicle??  I admire your restraint. someone, anyone make my baby bleed... that person would see the law up close and personal. there are zero excuses that are acceptable for anyone harming a child. 

Absolutely No. 

He can spend time with his daughter ourside of the house. 

There are no second chances for that kind of behavior. If she felt comfortable to do it once (and there were no real consequences) she'll feel comfortable to do it again. DONE. 

You may consider calling your daughter's doctor immediately- tell them what happened. Have it on record and build your case so that its documented that SD is not safe. Your DD's doctor may force his hand to see SD out of the home for your DD's safety.

Dump this dickhead and his failed family shallow and polluted gene pool.

smh

A 6yo who beats a 2yo sibling in my world would not be able to sit for a month.  I cannot even immagine the hell that would have rained down on me if I had done this to my younger brothers. (6 and 8 years younger).

Your DH is a failed parent and a ball-less POS.  

This is tricky because you don't know exactly what happened but if you gut is telling you SD is "off" and could be dangerous- start with cameras. They aren't expensive and are easy to install. I got a 4 pack on amazon for less than $100. I pay $12/month to keep storage monitoring for 90 days. They have SD cards that record about 2 days worth on their own, so you wouldn't even have to pay anything if you didn't want to.

(We have it as protection from accusations from SS17. He and his mother were notified that they are in the house and if they want to make a claim, it needs to be done within 60 days so that we can retrieve video- haven't had a single issue since.)

I feel like knowing that she is being watched will curb some of the issues right away. But if not, you may have to take more drastic steps.