My cousin is physically hurting my three year old, what do I do?

My cousin is 10 years old.
My daughter is 3 years old.

My cousin has been on and off physically hurting, and traumatising my daughter. I’ve spoke to my family member who’s fostered her but they are taking my cousin side saying “I’m bullying her”.

First:
My daughter has been pushed down the stairs, from the top floor (baby gate was there I made sure my daughter was safe) but suddenly I heard a tiny scream then loads of thumps before a loud scream and more crying
(my sister, told me my cousin opened the gate and pushed my daughter but my cousin kept putting the blame on my sister)

Second time:
My cousin fed her own urin, to my daughter and my other cousin who was younger at the time.

Third time:
I found bite marks all over my baby but I didn’t hear any screams or anything.

Fourth:
She bit her arms again

Fifth:
My cousin (apparently) sat on top of my daughter and squeezed her stomach twice.

Sixth:
My cousin grabbed my daughters face causing her to have scratches and my cousin also pulled the skin back on my daughter’s thumb.

I’m doing my best with this situation, but family members are telling me NOT to call the police, NOT to tell social services or that family member will loose three children to foster care.

(The children that my family member is looking after them is our nan, and the kids she’s looking after are her children’s both mothers of the children are alcoholics and crack heads)

I’ve tried watching my daughter like a hawk but my cousin keeps getting her when I’m either helping with dinner or feeding the pets.
I’ve asked my daughter to help but she always wonders off. I need advice, I am feeling so useless, I always miss when my daughter gets hurt.
My cousin is physically hurting my three year old, what do I do?
My cousin is physically hurting my three year old, what do I do?
My cousin is physically hurting my three year old, what do I do?
My cousin is physically hurting my three year old, what do I do?
My cousin is physically hurting my three year old, what do I do?
Updates:
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*I will be going to social services tomorrow*
My cousin is physically hurting my three year old, what do I do?
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