Flying solo with almost 4 yo

My parents really misses their granddaughter, and I’m thinking about flying solo with my child to see them. I’m little nervous about flying solo.

It will be 16 hours flight if we do direct flight. We flew intentionally before (twice), and many domestic flights. My child loves airplanes and flying. I’ve been asking her what she thinks if we go and see grandparents, but daddy stays home and watching cats. She is very positive about that, but I’m not so sure if she understands that she will not see her dad for two weeks (she is 3.5 years old now). She is very attached to her dad, who is doing 80% of parenting.

I’m also debating from two flight options:
If I fly out from my town, we have to do layover, but it will be evening/night flights. For direct flight, it departs at 1:30pm.

If you have some tips/advice for flying solo, I would love to hear them!