Fish get very anxious when they are on their own. If the goldfish are much bigger they may find this un-nerving as well.
A couple more females will encourage her out as she will hang round them. There are a couple of other things you can do. Add a couple more plants, which gives a feeling of security, also time is a great healer. The fish will get used to your presence. My fish now all come to the surface whenever I open the lid in anticipation of being fed, but I have had them for a while
Best be though, as everyone else said is more females. I am assuming you know how to tell the difference between male and female. In case you don't males have two anal fins and a small protrusion betyween the fins, while females have one single anal fin
HTH