Thanks for your response. I did talk to her after downloading the photos. She asked me to talk to her when she's alone. But when I went to her room when she's alone, it was locked and without a star icon at the right hand corner. I could still manage to give her the usb on the next day when she's alone somewhere else. But without talking to her alone in her room, the next quest Daphnee's Photos would not be activated. I'm stuck!
I don't know the specific scenario you are talking about, but basically let the stars and talk icons guide you.
Talk Icons are not indicators of new content, but on some occasions, a talk icon can also move the plot forward. Sometimes you also need a bit of time to elapse. (That is basically the "Grind" in this game. So there are very limited stat grind in the game, but there are some time grind. It's not excessive, mostly for 1 or 2 days)
If there are no stars to move the plot forward for about 2 days, try all the available the talk actions. Also remember to sometimes not sleep during the night. And remember to sometimes sleep in your room. Some events are triggered when you go to sleep.