For my axies, a lengthening of the amount of time they are exposed to light, coupled with a slight change in water temperature (only a degree or two) or a water change can set them off...Which is annoying when I'm trying to dissuade them until Midwinter.
I agree with the age thing Neil said- Mine didn't wait, and now I'm watching them VERY carefully to avoid long-term problems (My mum has forbidden me from getting more tanks, so no chance to split the genders out). More important is taking steps wherever possible to avoid overbreeding- an axie can lay well over a thousand eggs in a spawning, and you can just imagine the stress that would put on their body! My Molly has laid under a hundred in each spawning (Approx.60 at midwinter, a few at Christmas then nearly 80 on New Years, of which approx. 50 have survived (As far as I'm aware-My brother is taking care of them for me whilst I'm overseas). Goldie, on the other hand, has laid very small batches of under 20 eggs.).
If you want to encourage spawning, might I also suggest ensuring your tank is heavily planted with live plants and moss to provide your girl with a place to leave her eggs?
Hope you have success in the future!