Sorry to hear about the sibling
It's hard to know without a recording of the actual vocalization, but a distressed gosling will peep loudly and constantly.
How warm do you keep your home? And does she have free access to a heat lamp? Generally, it is recommended to keep the warming area for goslings at 90F for the first week, 85F for the second week, 80F for the third week, and so on until they have acclimated to ambient temperatures.
The water dish should be deep enough for her to submerge her bill in it. Geese tend to be messy feeders (although less so than ducks!), so they need a lot of water to clean out their bills. If her whole head fits in, that is fine as well. That should help her keep her face, and notably her eyes, clean.
I should have mentioned that you will need to cut the greens into tiny pieces. Geese normally feed by tearing at the grass, cutting it with the serrations on their bills and tongues, but if the blades are not firmly attached to the roots, they will not have any leverage to do so. As for the feed, there ought to be plenty of vitamins in the starter mix. And she will get plenty more as she transitions to a more natural diet. As long as she has access to many food sources, she should have the instincts to pick the correct balance. Just keep her away from the scratch grains! That is just goose candy