So opal is a Budgie, correct? Is she the only Budgie you have? It's completely normal for them to lay infertile eggs, but it is scary because of the risk of Egg-Binding, which is 100% fatal without immediate medical intervention. So it's important that you do everything you can to discourage her from laying more than just this clutch, as Budgies, just like Cockatiels, have a tendency to lay clutch after clutch after clutch once they get started, and then it becomes difficult to knock them out of it.
What is going to be most important for you to do for Opal's health is to ensure that her blood Calcium levels are high, and that she's taking-in enough calories every day, as they have a tendency to lose weight and become malnourished if they keep laying. So make sure that she always has access to BOTH a Mineral Block and a Cuttlebone at all times inside of her cage, if she doesn't already have both. The reason you want her to always have BOTH a Mineral Block and a Cuttlebone is because not only is the more Calcium she takes-in the better, so if she eats them both it's very good for her, but also because sometimes they prefer one over the other, so this way if she won't eat the Cuttlebone but she eats the Mineral Block, or vice-versa, she'll still be okay. Also, it's always a good idea to always have a dish of Egg-Food inside of her cage for her throughout the time she's laying the eggs, sitting on the eggs, and then for a few weeks after she's done with them. The Egg-Food is high in Calcium, but also high in calories, fat, etc. so it helps them keep both their blood Calcium high and their overall weight and nutrition up. You can either buy a bag of Qwiko Egg-Food from any Petco for $9.99 (I don't know if PetSmart also sells it in-store, but I know that Petco does, as that's where I buy mine), or you can actually make your own Egg-Food by cracking 2 or 3 large/jumbo eggs into a bowl (the whole egg, both yolk and white), and before you beat the eggs you want to grind up all of the full egg-shells into the finest grit/powder that you can (a mortar and pestle works great if you have them, or a little food-processor), and then dump the ground-up egg-shells into the liquid eggs in the bowl, and then beat the eggs. Then cook the eggs with the added ground-up shells mixed in, just like you would when making scrambled-eggs, let them cool, and then chop the cooled scrambled eggs into the smallest little bits that you can for her. If you've ever seen a store-bought bag of Egg-Food, like the Qwiko Egg-Food that you can buy at Petco, it's basically what I just described ground up into tiny little bits so that small birds, like Budgies, can easily eat it...And they usually love it. I've found that making sure my female breeder Budgies always have access to a dish of Egg-Food from the moment they lay their first egg until about 2 weeks after they are completely done with the entire process keeps their Calcium up much higher than it would be with just the Mineral Block and the Cuttlebone, as well as keeps their weight up.
***As far as keeping her from laying clutch after clutch after clutch, it's all in how you handle this first clutch that she's laying now. I'm assuming that since she's only laid a single egg so far that she's not yet laying on it. It's extremely important that you DO NOT ADD ANY TYPE OF NEST-BOX OR ANY TYPE OF NESTING MATERIAL TO HER CAGE!!! So don't put anything in the bottom of the cage for the eggs to sit on, that's a huge no-no because it can trigger her to keep laying more and more eggs. Just allow the eggs to sit on the grate on the bottom of the cage as she lays them. If she happens to lay any in her food dishes then just take them out and put them on the grate with the others; you can help her to keep the eggs together on the grate, you're not going to do any damage or keep her from wanting to lay on them by touching them. She probably won't start laying on them until there are at least 2 eggs, possibly not until there are 3. Since you have no male Budgie you don't HAVE TO boil or freeze the eggs and then put them back in, though sometimes people do this anyway to keep the eggs from rotting, but I've not ever had an issue with infertile eggs rotting in the short 21-day incubation period...What I mean by "incubation period" with an infertile egg is that what you're going to want to do is allow her to lay on this clutch of eggs, simply on the bottom of the cage with no nesting-material at all, for as long as she wants to. Since the incubation period of a Budgie egg is about 21 days, she'll probably continue to lay on the eggs until each one of them is around 25 days old or so. And you're going to just want to let her lay on them for as long as she wants to, until she realizes that they aren't going to hatch and she loses interest in them, and she stops laying on them. At the point when you see that she's no longer laying on them at all, then you just grab them and pitch them, and hopefully that's it. If you have no nest-box, no nesting material inside the cage such as bedding, wood chips, no cloth/towel/clothing, nothing at all inside that cage that can be used as a nest, and she is allowed to lay on the eggs until she naturally wants to stop herself, then hopefully that will knock her out of breeding-season and that will be it.
***Budgies usually lay an egg every other day. So keep an eye on her, and if she lays an egg and then two days later she doesn't lay another one, keep a close eye on her. Sometimes it can be every two days, but no longer than that typically, so at that point you want to very, very gently pick her up and look closely at her abdomen and see if it looks like she's carrying another egg. It's usually very easy to tell in Budgies whether they are carrying an egg, as they are so small that the eggs take up their entire abdomens. You can very gently feel with a single finger on her abdomen for an egg, but do not ever push or press-in, as you can easily rupture the egg inside her. What you're doing is trying to make sure that she's not Egg-Bound. If you see her "straining" to lay an egg, which looks the same as if she would be straining to poop, that's a Red-Flag that she may be Egg-Bound and absolutely must get to an Avian Vet immediately, no excuses or waiting, it's not optional, as Egg-Binding will kill them without medical intervention within a couple of hours.
Ask any and all questions here that you may have. There's no such thing as a stupid question when it comes to your bird laying eggs.
