From what you've said, I don't dispute that your mother loves your dd but it seems to me that her motivation in obtaining a residence order was primarily financial because, given the absence of social services in the proceedings, she could have cared for your dd on an informal basis until such time as your condition was under control.
Given that I've reached this conclusion based on 3 posts from you, I have some confidence that others will form similar a similar opinion especially as, as I've told you, your situation is not uncommon
However, I note that on babyhammock's post re CAFCASS you have made the comment that you believe that this organisation will have 'met its match in you'.
I would advise you not to take an antagonistic approach to any conversation or meeting you have with any CAFCASS officer as they are NOT your enemy at this point in time.
When interviewed, relate the whole history, as written by you above, in the same calm and factual manner as you've told it here, and provide copies of your supporting evidence - NHS/SS/CSA records etc.
In reaching judgement in this matter, the Court will take into account your dd1's wishes and in this respect CAFCASS may well prove to be your friend.
Has your dd1 expressed a wish to live with you and her half-siblings? If so, do you know whether she has made her wishes known to your mother?
On a separate note, I'm curious as to why your mother was allocated a 3-bed council property. Do you have any siblings that were living with her at the time she was rehoused?