Now that I look again, she seems a bit thin :/ and most of the adult mice I get tend to be a bit small Ahaha

I'd go to Walmart and buy a kitchen scale. They're only like $20. Feed 10-15% of her body weight every 5-7 days.

Since I feed mice (no one eats f/t so no option of feeding rats as live ones are illegal here) I feed every 5 days. >_>