Cat's suffer from anorexia, and the number one cause is something traumatic, like moving. I'd bet she's drinking normally, but if you can try to feed her a little more than the others. Staying with a cat while they're eating, and stroking their back is a way to promote eating, and 3-4 extra minutes per meal is a very good investment. As long she's drinking properly, you can do this without vet care, but if she's NOT drinking, take her in ASAP.
I would take her to the vet just to be sure she is OK.
My cat has a hyperthyroid condition that keeps her too skinny. She is 12 and weighs less than 6 pounds. Very healthy and active, tho.
Maybe she missed where you used to live and so she's a bit depressed??? Idk
she is underweight. You might try a deworming regimen first, then some canned cat food. If that don't help, a trip to the vet is in order.
she might have parasites or be stressed out about the move. Needs to be checked by a vet.