She needs a checkup by a good primary doctor and a good psychiatrist. Get referrals from people you trust.
From my own experience, I would not recommend a psychologist who can miss the point completely. They might draw her out, however
Depression is so common today that you are right to avoid jumping to the conclusion that this is what's bothering her.
The "silly" behavior does hint of bipolar or drug use. I would have been grateful to have gotten help decades earlier. Bipolar 2 so hard to diagnose.
I think you are a wonderful parent.