Few day old duckling

I have a black crested duckling I got Thursday April 7th she wasn't eating or drinking I brought her in the house with another one ande started to mix feed into a cream of wheat consistency and she started eating. It started with crusty eyes and couldn't go to the bath room now her eyes aren't crust you she's eating solid food along with the mix still and drinking water she pooped on me this morning so she can now go to the bathroom . When she stands up she will flop over and not get back up for s while what could be causing this and what can I do to fix it