2 days is not bad. Marans should not be smaller than Wyandottes. I wonder if she is something else or maybe a bantam??? Time will tell.
To me that sounds encouraging. Wishing you the best.
Do you know how long they were in shipping? That might give a clue as to if it is shipping stress. Some chicks hatch with birth defects and are just not meant to make it.
But regardless I would not wait. Some people use electrolytes or something they can get at the feed store. Some use...