If you are wanting another budgie for yourself as well as for her then I would suggest getting another one. But I would suggest that at least at first you plan on keeping them in separate cages. Birds do not have to be in the same cage to offer companionship to each other. The cages (after quarantine) could be set up beside each other, then if the female seemed interested in the new male you could introduce them in a neutral space or cage and see how it works, if she pecks at him instead of being receptive to his companionship then keep them separate and you can still have them both for feathered friends and as separate companions to each other.

If you are getting a new bird for your other bird only and not as a companion to yourself as well then I would not suggest getting another bird. If your female has not show interest in companions she may be quite happy without one. As you said she is showing more "happiness" since her mate is gone. It is possible that after being left alone without a mate and without real handling that if you approach slowly and patiently she may even be receptive to taming or training. Circumstances do change a birds personality and she may be much more content without a mate.

Unless you are a breeder and planning on having a houseful of birds or have homes to give babies to I would not suggest getting a large group of budgies as they will take more time to take care of and have less chance of becoming friendly to people. (I do realize some people have whole aviaries full of "tame" birds but this is rarer than having an aviary of breeder birds that are not as receptive to human contact.