I would give her a small dish of the calcium citrate. She will eat it on her own and is unlikely to overeat on it. Do that for a couple of days then switch over to the oyster shell.
If she's huddling under the light, then she's cold. It's okay if most of their cage is a bit cold for them as long as you make sure that she has a corner where she is at a comfortable temperature.
The mineral grit is unlikely to do any harm. If they eat some of it it will just serve as grit in their crops and help them digest their food. My buttons have plain old garden dirt as bedding.
If she's huddling under the light, then she's cold. It's okay if most of their cage is a bit cold for them as long as you make sure that she has a corner where she is at a comfortable temperature.
The mineral grit is unlikely to do any harm. If they eat some of it it will just serve as grit in their crops and help them digest their food. My buttons have plain old garden dirt as bedding.