what does the phone hint for this quest say? and do you have any other quests active?
since you also have gathering storm active, i'm guessing isabelle has hidden while you try to lure spinach outside the school — which is why she's not available for you to quest in twisted desire.
the game can't recognize which quest you're currently doing, so this issue happens sometimes. but i have a hotfix for you: https://drive.google.com/file/d/1hQ9tILDO0J_4PCUYMJq0HTswl3zM8twK
please download this file, then drag it to your \AnotherChance-v1.17.1-pc\game folder!