Any 4-5 year old who is available for adoption with have suffered many loses, many placements and probably abuse and neglect. They WILL have issues. These will impact on your DD , her school and your friends and family.
You need to be prepared for this, and to always put your DDs needs second to your adopted child. This is what your agency will expect. They may talk of balace but its impossible as any new child will be very needy.
If your DD really doesn't want a sibling who is not your bio child, you woudl be very unwise to preceded and you won't pass the assessment anyway
It's easy if you are a social worker to think that you know what it might be like to deal with the issues that abuse and neglect bring. However, having read about it, been to a lecture or even met a child with these problems once a week for an hour is not the same as living with it 24/7 and having to deal with the impact it has on others and yourself.
Most of all,you need To understand that once you become an adoptive paremt, everyone you deal with professionally will blame YOU for your child's problems.you will move from being seen as a profesional who is part of the solution to being a bad mother who has caused the problem. It's hard to understand the psychological impact of this.
This is very VERY hard for those who have dealt with children in care on a profesional basis and then go on to adopt. Ive seen it split up marriages and destroy careers.
You need to knwo that approx 50% of the adoptions of school aged children break down. How woudl that impact on your DD, your marriage, your wider family and your career?
I'm sorry to sound so negative. But this is a really REALLY hard thing you are thinking about doing, and you woudl need to be 100% sure you wanted it and were prepared for the costs as well as the benefits. As others have said, you can't do it for someone else.
I understand this is a sensitive subjec, but you mentioned that you had a hard time re covering from a miscarriage.if you mean that you had depression,you need to be aware that post adoption depression is sadly very common. Also it can be triggered by the stress of the assessment and by having a new child placed. adoption is not an " easier " way of having a child, without the risks of pregnancy and birth.itbrings much higher risks.
So any history of mental health problem will be explored as part of your assessment. Of course , if you didn't mean that you had depression, this isn't relevant.
If I were in your situationand wanted another child, I would consider another pregnancy . Unless by " age " you mean you are post menopausal. If you just mean you are in your 40s, that's not too old as you will see if you read the TTC boards here.
HTH