I have observed that kids will get kind of silly/giggly/maniacal when they are really uncomfortable. For example, my daughter, 16, was telling me about a truly disturbing murder she read about, and she kept grinning and stifling a giggle. I started to chastise her for it then remembered this is a common thing when kids especially feel intensely uncomfortable. It's a coping mechanism. It's not necessarily a bad thing, just a coping thing.
Your mama instinct is king. You know something bothered her. Your job is to back off, let her know in a very simple, age appropriate way that you two can talk about anything, then let it go for now. Maybe she was just wound up and/or uncomfortable around her dad.
You might tell her a story about a similar situation you got into when YOU were a child her age, and reflect what you saw in her in yourself ("I was so wound up and silly after I visited with my dad that I ran all over the room! I wonder what I was feeling?") This can help her share her feelings with you without feeling put on the spot.
Two of my kids were adopted from foster care at ages 8 and 9. They lived through HORRENDOUS neglect. Their mother was severely mentally ill and thought they were Russian spies and space aliens. She was incredibly cruel at times, also loving. Sometimes I overthink the trauma part of their lives and make things into more than they should be (see story of grinning daughter, above) when I should just relax and let them simply be kids. As my mother would say, "Don't borrow trouble!"
You are a good mom. Don't be so hard on yourself. You were smart to get out when you did and acted in their best interests.