I can't help you with much on breeding, but no, eggs can absolutely not be fertilized after they have been laid. So if you're sure that the eggs she has laid are not fertile then they will not every be fertile.
Just an FYI to you, you do not need to "get your female a male" and breed her just because she is laying infertile eggs and is "digging in her tank", she doesn't want to be bred, she just wants to have a laybox with damp sand to lay her eggs comfortably. Do not breed dragons unless you know what you are doing and you want to breed them yourself. And I'm sure you know that the market is absolutely flooded with baby bearded dragons everywhere, in pet shops, online, everywhere, and unless you're breeding some very expensive morphs or colors you're not going to make any money breeding normal bearded dragons, nor do we need more babies. I suggest that you check Craigslist to see how many bearded dragons need homes across the country, there are literally thousands of them that people are trying to rehome, and thousands of people who bred babies to try to make money and they can't unload them. And bearded dragons are solitary animals and should not ever be housed together, only multiple females can be housed together successfully and even this usually ends in domination and violent aggression. You cannot house 2 males or a male and a female together (I certainly hope you are keeping your male and female separate in 2 separate enclosures, otherwise the male will breed her literally to death, or they will kill each other, guaranteed, they should only come together for short periods of time to mate and must be supervised the entire time). So if you breed them you could potentially end up with literally dozens and dozens of babies that you cannot sell...can you afford or for that matter do you have space to buy each one a complete setup?
I'm not trying to lecture you at all or be harsh, but you said "don't worry, I did lots of research first", yet I'm sorry, not to be rude, but simply asking the questions you just asked proves that you don't know nearly enough to breed dragons. Again I'm sorry I don't mean to offend you or criticize you, but if you take a look at Craigslist and go to "Community, Services, Pets" and then type "bearded dragon" into the search bar, you'll see why no one should be breeding normal baby bearded dragons at all...and that's only Craigslist, that doesn't account for the thousands of normal babies across the country in all the Petco's and PetSmart's, which sell normal babies for $40! You'll never make a profit if you're buying adequate amounts of live insects to feed multiple babies every day, not to mention the multiple lights, supplements, etc...so be smart about this please....