my first born hates my pregnancy

I'm in a bit of a dilemma here.... My first child, who has always been the center of our world, is not excited about the arrival of their upcoming sibling. In fact, they’ve expressed feelings of jealousy and fear of losing our attention. She is 3,5 yo now... We’ve tried to involve them in preparations and talk about how exciting it will be to have a new baby in the house, but nothing seems to help. They’re acting out more and becoming increasingly clingy, which is starting to worry me. Her reaction to my second pregnancy is quite concerning. Once she was patting my belly... I thought she finally changed her mind... But instead she said, "UGLY BABY, you should just die, little baby"... What should I do? I was so surprised, not knowing where those words are coming from. How did you handle introducing a new sibling to your firstborn?