How can I put weight on our new Great Dane???

We recently adopted a Great Dane ...she is 8 months old and she was severely malnourished and crated 22 hrs a day....the previous owners would leave her kenneled up to three days while they went on business trips...needless to say she is very shy and jumpy...she does have a great appetite but it just seems as active as she is the weight just wont stay on??? Any suggestions??? We adore her!!!