Hello
and Welcome To BYC! Sure sounds like you have a broody! Good luck with the hatch! TwoCrows gave you some great advice and links. If Evelyn started sitting on the 18th you should have chicks hatching around April 8th, though they can be a day or two early or a day or two late. If you only have the two chickens, you can probably just leave her in the nest box where she is to brood. One other thing to take a look at is where the the nest box is, if at floor level it should be fine when the chicks hatch, if it is off the ground you'll want to do something so the chicks can get in and out.
and Welcome To BYC! Sure sounds like you have a broody! Good luck with the hatch! TwoCrows gave you some great advice and links. If Evelyn started sitting on the 18th you should have chicks hatching around April 8th, though they can be a day or two early or a day or two late. If you only have the two chickens, you can probably just leave her in the nest box where she is to brood. One other thing to take a look at is where the the nest box is, if at floor level it should be fine when the chicks hatch, if it is off the ground you'll want to do something so the chicks can get in and out.