You can simply say that: "You seemed off the other day. I hope you're okay". That doesn't sound bad. Just caring amd concerned.

I know it's scary when your T doesn't have it all together. Oye, with L. Maybe she didn't tell you anything because she didn't know? Like let's say she had a bad night, but put herself together and felt okay. Maybe you could see evidence of the bad night, but she didn't. Could it be something like that?