Hi JoAnn! Yes, that is very possible. Usually it's 2, but as long as her vent is not swollen (the under-her-tail-area doesn't have a bump) then she should be fine! Lovebirds usually 2-5 eggs, laying 1 every other day. Since you have a male and female are you hoping for this egg to be fertilized? If you don't wan't a baby bird, you should probably remove, boil it, let it cool down and then put it back. Also did you give her a nesting box? or where did she lay this egg? And (sorry for all of the questions) is she sitting on it/brooding?
9 months old is a little young however...Make sure that she is getting egg food and calcium supplement! Laying eggs really takes a lot out of the little birdies!
Thank you for your response, she and my male have a large ceramic pitcher that is perched on top of a bookshelf an inch or so below the ceiling which they have been nesting in since she could fly (I know, crazy, but my birds are "cage free, free range" and very active and happy). A proper nesting box is coming tomorrow which I will introduce them to. Their current nest is filled with nesting cotton, organic botanical hay which they carried and set up themselves, as well as shredded newspaper. Their nesting box will be placed in their cage, along with their current home for safety. My male is feeding her, she is brooding but still going to their cage a couple of times a day to eat and to get more hay to put in their nest. She looks bottom heavy, no distress, not egg bound, will check for a second egg tomorrow...I just was not sure, since she is so young, if it was normal to only lay one egg. They eat a variety of pellets, millet, some nuts, seeds and dried fruit, egg, fresh kale, lettuce, apple, lettuce, lots of variety fruits and vegs. Very spoiled, social and very happy. Hope that helps, and Ivwill do what's best for them. Thanks