She looks rather young. Can you approximate her body size - in cm or inches? Compare her to your male - how small is she? If she is about 2/3 or more, you can probably breed her - though risky. But if she is less than that, it'd be best to wait a bit longer.
That's big enough. 3.5cm/1.5" (body only) is big enough.
..... your male is 1" larger? .... are you including the fins? Approx the body only, without the fins. Long finned males may look a lot longer but their body may be not much different.