Disrupting our 3 year placement

We’ve had our FD since birth, it will be 3 years in April. The last two years have been very challenging with behavior, and it’s increasingly getting worse. She screams constantly without verbalizing her needs. She has started hitting me and my youngest bio child (18 months). No discipline is effective. She screams constantly during the day. She goes to bed screaming, wakes up in the middle of the night screaming, and wakes up screaming. I can generally sooth her at night, but not so much during the day. It’s all consuming and very exhausting. She is now at an age where we can start getting her evaluated for things. she is a bit speech delayed, she’s been in speech therapy for a year. She’s in daycare, and they don’t experience half the behaviors we do at home, so I’m assuming it’s our home that’s triggering her. Our bio kids are easy going and mild mannered, so I’m not sure what we are doing wrong with her.I feel like perhaps we aren’t a good fit for her, but we are all she knows. She has never had an bio family in the picture, zero visits with bio parents. Her TPR is scheduled for 3/29.We’ve communicated our struggles for almost two years with our agency and they weren’t much help. Now that we’ve explicitly stated we are considering disrupting the placement they are scrambling to help. We feel at the end of rope here. It’s hard to enjoy her when she’s in a good mood at this point. Yet, I’m having a real hard time pulling the trigger to disrupt. It’s hard to share this stuff with friends. Most don’t understand disrupting a placement.. especially one you’ve had for 3 years.