What is the temp in your brooder? If it’s steady at around 85 they should be okay in the garage. All duckling sling their feed my Runners are adults and big slobs when it comes to eating. are you using any niacin with your ducklings? Scrambled egg is very good for them. You might try adding a little feed in with the egg so she is getting some of her feed to. Start slow and add more as she is eating more.