I'm sure it had nothing to do with you or what she thought you may do, mad_lili. As Gill says, some cats find the action of being sick quite unnerving, and a cat's instinct when it is vulnerable is to make itself less vulnerable - usually by hiding. The best way to approach this is to stay calm yourself, almost ignoring her reaction - if she senses anxiety in you over what happened, that will reinforce her feeling of fear, so if you stay calm and unruffled, she'll know that she can come to you once she's feeling braver, and you can administer cuddles and reassurance aplenty.
When we first brought Moray home, Moray would run and hide, peeping out at us from his concealed place after he used the litter tray. He always looked very nervous and skittish. However, we suspect that was because he had been yelled at and told off in his previous home, which hadnt got him and his sister off to the best of starts. He very quickly overcame that though, once we would praise him for using the tray and show him he'd been very clever as we admired his handiwork (
the things we do....
)