Try to positively guide her - make it as positive, enjoyable, etc. The more fun you make it seem, the less you push, the better or she may think you're being nosy. If you're worried about her birds not getting attention when the foal is born, then perhaps encourage her to get 2 more budgies in their own cage, or maybe upgrade the cage for her budgies to something bigger (a flight cage) and tell her she can then put another pair, maybe even 4 more birds in it. Getting one more single budgie is unfair to that budgie - he won't have another budgie friend and if she introduces him/her to the other 2, they will probably bully him/her and the single bird will be the odd man out.
If the bird has a friend of the same species, toys, good food, and fresh water then it's not so bad - I know we all want our birds to have the ideal life with loads of enrichment, human contact, out of cage time, etc. But for some that's not feasible and some just don't see birds that way, they are more hands-off pets.
I know I may sound harsh or negative, but I'm trying to play devil's advocate and show the flip side as well. Having worked for many years in the pet industry, you learn to appreciate those who will at least give their birds good quality care, if not the ideal quality of life. Really, if they are in a cage where they can get enough exercise, they are getting good food, fresh water, and have eachother for companionship, it's really not that bad that they don't get human interaction.
They are birds, not humans, as much as we empathize and put human characteristics on them, something we are all
Many prefer contact with another bird rather than humans. and if they are not hand-raised, then they know other birds as their primary friends and companions. Humans are fun, but kind of scary, and they'd prefer to be with someone who speaks their own language and can interact with them in ways only another bird can. That's why so many people keep their birds in pairs, even at the sacrifice of their 'tame-ness.' I did that with my linnies, Mizu chiefly, because she liked to interact with me but was so hand's off I wanted her to have a friend to snuggle with, preen, and really bond with. They get some out of cage time, but no real direct interaction with me. They frankly don't want it
Both were hand-raised, but were both introduced to another linnie at a very young age and much prefer one another's company over mine. They will eat snacks out of my hand and Loki will talk with me, but that's about as far as it goes. And that's just fine with me - they have a huge cage, they get great food, clean water and are in the peak of health.
I hope all that makes sense. Just try to guide your friend in the most positive way and remember - if the birds are healthy and have a friend, then they are happy and will be OK without her direct attention or interaction. I would encourage her, like I said, to focus on maybe getting another pair of budgies or encourage her on the importance of rotating toys, foraging, etc so that even when she can't play with her birds they can entertain themselves and will still have a lot of fun