Like everyone else says, if you can prevent a female from laying eggs, you should! Laying eggs is immensely taxing for the female - it pulls huge amounts of resources like calcium out of her. You also risk issues like egg binding, which is when an egg gets stuck and is very hard to treat. It can be fatal. Laying eggs also means that a bird is likely to be hormonal and more unpredictable in her behaviours.
Take the nest box out and make sure she's getting enough dark, quiet time.
If you want to know whether you do have a female or not, DNA testing is much more reliable and doesn't come with health risks. Some tiel mutations show sex-based differences (like the presence of pearls in an adult).