What should i do for my lonesome parakeet?

So basically I had two female parakeets, a blue one and a green one, about 3-4 years old, both bought from a shop once they had already developed but were still fairly young. This of course means they had distinct personality traits that existed before we got them. The blue one is a funny bird, always playing with toys in its cage and trying to get in your hair. She will gladly perch on your finger if shes in the mood to play and seems to enjoy nibbling everything nonstop, from her cage walls to your fingers. On the other hand, the green bird is and always has been incredibly nervous. Just passing by the cage gets her ready to run. Sometimes you can get her onto your finger but that just makes her stare at the cage, looking for a good opportunity to get back to it. She never bites, i have never seen her play with any toys, and she doesn't care for mirrors. The two birds got along alright. Not great, but the blue bird is all that the green bird had as a companion. I'm worried because the blue bird managed to escape recently which baffles me because we've left the patio door wide open without either bird going near. (she was probably trying to land on my shoulder while i happened to be walking out the door). Not only do i really miss my bird, but i think the green one misses her too. She chirps more than she ever has and theres nothing to respond back. What should i do? I would like to play with her but shes much too nervous, definitely not suited for the wild, and placing a new, younger parakeet in the cage doesn't seem right.