Lost on what to do

Absolutely lost on what to do. I’ve had this young Thai constellation for over half a year now. She gets both direct and indirect light everyday and occasionally will sit outside on my balcony. Last month, I finally dealt with thrips for the first time ever and of course it was with my Thai constellation. I initially washed the leaves with dilute castille soap until my dead bug spray came in. I’ve been liberally spraying her with Captain Jack’s deadbug brew once a week for the last 2 weeks. She was watered about a week ago and I washed her terracotta pot down with dilute castille soap to wash off possible fungus and mineral buildup. She gets watered every 2-3 weeks. She was healthy as a horse until a month ago and now she looks absolutely pathetic. I have no idea where these black spots came from. Today I’ve noticed her lowest leaf is mushy at the tip. As for the thrips, no larvae can be seen but her leaves are probably getting more yellow. What am I doing wrong?

She only has 4 leaves and none are healthy so I have nothing left to chop off. I don’t want to give up on her.

Last photo is a reference for what she looked like prior to all this.