Is my Zebra Danio bullying my Serpae Tetra?

I have a 5 gallon tank with many hidins for my fish like caves, plants and rocks. In the tank I have a zebra danio and a serpae tetra. The Tetra usually stays to the back of the tank behind some plants, but most of the time when she comes to the front, (even to eat) The danio will chase her away and sometimes it appears as though he nips her tail. I noticed that she rarely retaliates. I'm keeping a close eye on the condition of their fins and nothing seems to be torn. I am worried that she is stressed or she is not getting enough to eat. Is this normal? What should I do?