I remember being scared of the toilet when I was little, lol. I thought something was going to come out of it and get me when I flushed it or something.

Maybe try slowly getting her more comfortable with it. e.g. take her in there and show her the toilet, get her to touch it, hold her and flush it, get her to press the button (maybe make it seem like fun). Do these slowly over a few days and see if she can get used to it??