What does she know about her adoption? Does she not understand that you are there forever and aren't going away? You might talk to other parents with adopted older children and see how the adoption played into different stages. Some kids are just not bothered by it at all and some think very hard about it and feel a sense of loss.
OR it could just be her dealing with first grade, which is different than K, and being a little more moody about changes.
Whatever the root cause, she seems to need a lot of reassurance about you in her life.
I'd also try talking to her. I was shocked to find out that my 4 yr old thought I stopped loving her while she was in time out. I don't know where she got that idea. I told her I love her all the time, even if I don't like her behavior all the time. Maybe it's something simple that she's gotten into her head that needs to be corrected and you don't know til she tells you.