If she's tame, then she probably just needs time to settle in and be more comfortable. They don't necessarily need to be in pairs, they just are very social birds. If they are tame and someone's home most of the time, they do well as only budgies. But if they will be spending hours a day alone in a cage, or just aren't tame enough to enjoy interacting with people, then they really need another budgie friend.
For now, I'd focus on getting your budgie settled in and see how she is in another week or two. I wouldn't rush into a new budgie - in part because most pet store budgies tend to be mass-produced and often unhealthy. If you decide to get another one, it's well worth a bit of a wait to find a breeder you like. A male would probably be safest, as female budgies tend to be very bossy and sometimes aggressive.