we live in washington, and i think one of my hen sitting on a nest,is it the wrong time of year for babies to be born.

I have seen hens come out of the barn on Jan 1st with a clutch of babies there is never a wrong time in nature just inopportune blace her in a coop with her youngins and she should raise them fine.

One consideration you might look at would be the conditions in your area when they are hatched. If it will be very cold, the chicks will have to spend most of their time underneath biddy and most of her energy will have to be spent keeping herself warm. If she will be in a relatively warm area of a building, or if you provide some artificial heat, she will be able to get her chicks out and about and be less miserable, too. The bottom line might be: will the weather permit her to do the things she needs to do once the little ones emerge? Where we live, baby chicks this time of year would not be a good idea. If you discourage her from setting now, she will likely try to do it again when the weather warms up in the spring, or perhaps another of your hens will.