Why is my platy fish sitting at the bottom of the aquarium?

Yesterday, I bought 2 platy fish for my new aquarium. One is a white-pink male and the other is an orange female with a black tail. When I got home, the male was swimming around and the female was just sitting in the back corner. If the male gets close, the female bumps into it and chases it away. Also, when I fed them, the female still stayed at the bottom, while the male came to the top to eat. Why is she acting like this? Any help would be greatly appreciated. Thanks.