Just keep an eye on her and she will be fine when she stops pasting up, not the most helpful comment but that is really when you know.
Pasty butt is not contagious but it is not only caused by shavings. It can be caused by stress, which is why it's a common ailment for shipped chicks. If the temp in the brooder gets too high or too low for a prolonged period it can stress them and cause pasting. Certain other things that they eat can stress their system and cause it. It is essentially a form of constipation.
Adding a small amount of molasses to the water will help pasty chicks recover quicker. Mix it so the water looks like a weak tea.