Why is my dog wailing at my other dog?

Two dogs, one a rat/chihuahua(Blinky, he, 3 years) the other lab/retriever(June, her, 1 year). We have had June for around 2 months now. She hasnt been aggressive from what we have seen. Some bone aggression, but not much past the first month. She has played with other dogs her size and doesnt wail, if any it's very quiet or minimal. With Blinky it's full on wailing, they will start playing(tails wagging and everything) then she will start wailing at him as they play bitty face(nipping ears and face of each other). When they are outside she will wail in a deep voice, almost growling. Again we haven't seen them fight, but I'm scared that they will if I just let them continue. Not all her wails are deep, but I'm still worried.