First of all i'm going to give you a quick sum-up of degu care
A minimum that i have used for degu housing is 13x25 which isn't very big and would only cost about $20 off of craigslist or from a simple pet store. That size will work great for one degu as long as you give him time out of his cage every day. Always have wood and cardboard available in the cage so they can trim their teeth or she may drive you nuts chewing on the bars of the cage. They are best in a plastic-bottomed wire cage (such as something you'd keep a guinea pig in). They normally love to climb so try putting a branch in there for them to run around on. I always provide one good-sized hide for them to sleep in along with some cloth. I keep one of my baggy used shirts in there for them to cuddle with. It provides comfort and a sense of smell from you. Always provide plenty of toys so they don't get bored. Little wooden treats, balls, ropes, hammocks, and other ect stuff works great for them.
Guinea pig food is a good semi-supplement for them and will keep them healthy. Try to make sure it is Timothy-based as that is healthier for them. Actual degu food is even better yet. Be careful when feeding them though because only a limited amount should be given per day to ensure they don't get overweight with diabetes. They get diabetes easily. I usually give mine a small handful every day and that keeps her at a pretty good weight.
As for treats... they should be used for just that... treats. For training and socializing. In little moderation, broccoli, green beans, dandelion leaves, fresh mint and parsley, carrot tops, cauliflower, asparagus, celery, and lettuce are good. I wouldn't feed a lot though. Okay for once a month feeding, peas, carrots, apple, cucumber, and cherry tomatos. A weekly treat can be red or green pepper, radish, instant oatmeal oats, and soda crackers. Again, be careful with feeding them these as fruits are high in sugar.
Hay is also very important. It is best to feed them Timothy Hay in unlimited amounts as it's good for the digestive tract.
Always supply plenty of water. They will drink from a bottle but I do notice that adult degus prefer a bowl but the bowl needs refreshing at least twice a day to maintain hygeine.
Never pick them up by their tail or squeeze them. A simple know-all with rodents. Scoop them up instead of grabbing them and give her plenty of time outside of her cage. They do do better in pairs but if you give her plenty of attention until you can get her a friend, she will do fine. If she was previously housed alone she should be used to it and will do fine as long as you provide plenty of love every day. Mine lives single and I take her out for about 2 hrs every day and she is perfectly content on her own.
In the meantime, if you are not interested in the care for her, look into selling her to someone who knows degus and will provide plenty of love to her. Hope this helped