Her face was as pale a sheet simile or not?

That's a classic simile! It's a very common and effective way to describe someone's extreme paleness.

Here are some other ways to describe someone's paleness, with and without similes:

Similes:

* Her face was as white as snow.

* Her face was as pale as the moon.

* Her face was as white as a ghost.

* Her face was as pale as a lily.

Without Similes:

* Her face was deathly pale.

* Her face was unnaturally white.

* Her face was drained of all color.

* Her face had a sickly pallor.

The choice of which description to use will depend on the context and the desired effect. "As pale as a sheet" is a strong and evocative image, but it's important to choose the simile that best fits the overall tone and meaning of your writing.