Even if you don't like writing, I can say with confidence that you will never regret and someday greatly appreciate an effort to keep some kind of regular record of what it was like to be a birthmother. For that matter, other members of the birth- and adoptive families can similarly gain from it. My advice would be to start writing right away. Her child can look at it someday and know more about his or her mother and the beginning of life as a child of open adoption. Society is becoming increasingly aware of the special needs of adopted children to demystify their births, and this is a great way that all parents could help them do that.
All writing is unique.
They never happened before and never will again. However, most people have preconceived notions about the act of writing that prevent them from writing journals because they think their style is wrong, their words sound stupid or boring, or their ideas simply are not valuable. But these notions, no matter who holds them and for whatever probable justification, are invariably wrong. It can be written, set aside, and never looked at again. Even if that becomes the case, journal writing will have been very helpful as a mental and emotional processing tool.