Thank you for the advice! I definitely see a bump on her lower abdomen, not right at the vent but just above it. Vent itself does not appear red or swollen. She is still actively hopping about, chirping, eating etc. When it's sleepy time, she sometimes goes from one foot to the other or sits with her belly close to the perch presumably because of her weight.
What does a straining budgie look like?
If an egg is laid would it help to put the male in the cage with my other female budgie in terms of discouraging Lily to lay more eggs?
How long should I wait before having her checked out by the vet?