I myself have a lone degu, his brother passed away and we couldn't get a new one because no vet around here will neuter a degu. So instead of trying to introduce two adult males, I just spend a lot of time with him. If anything we are even closer now. Although you should have more than one degu, if you absolutely cannot get another one then you will simply have to spend more time with him/her. However since this one is a young female I would advise to do like everyone else said, get her a new female playmate as soon as you can.