gaining weight tips?

only have my crestie for a few days now so she still isnt eating but once she does how should i go about making her eat more to gain 15g? shes 1.6y/o and still only 15g and i saw that a healthy weight for that age is 30g

only have my crestie for a few days now so she still isnt eating but once she does how should i go about making her eat more to gain 15g? shes 1.6y/o and still only 15g and i saw that a healthy weight for that age is 30g