Hi!!!! Thanks for asking!!! <3
Ilztavin's pretty much a master at keeping her emotions secret. Deception is one of her most perfected skills. (She's a charlatan after all. :D) She never displays having stress, or anxiety.
Sometimes, she takes the great old spellcaster way of getting the stress out her system: finding a hidden spot at night, casting silence on herself and shouting into the void for some minutes.
In "peaceful" times (drow standard), before the events of bg3 and the loss of her House, Ilzt lived a quite busy life. She always had work to do. (House wizard stuff, being the Matriarch's manipulative little right hand, trading stuff, inhouse politics.) So, being at peace, or relaxing wasn't often an option for her. She finds resting difficult.
If she has to spend her time with something not work/adventure related, she loves having a good board game session (or more like a Gale and Ilzt quarrel session), card games, reading (a lot, she's a wizard after all) and doing origami.
After the events of bg3, she has a hard time fitting into the peaceful life in Waterdeep. She often feels bored, and the lack of things to do makes her quite depressed at first. But then she finds new (not always approved by the law) ways to get herself busy, so everything turns for the better again. :)