By the size of the gravel in the OPs pic, it appears to be small, too small and young to exhibit outward gender difference.
If the gravel is large, and the fish is actually 5" or more I'd agree with Jexnell that it looks female, by the shape of the profile, although to me these Red Devil type Amphilophines are notoriously hard to determine sex of, even as full grown adults. I've seen females with nuchal humps, and males without