Are my gerbils fighting?

I got my female gerbil from Petsmart exactly a week ago. in the store, she lived in a tank with two other females. for her home now she has a ten gallon tank with a tank topper on it. i decided to get another gerbil so that she wouldnt be lonely, and i got the new gerbil from the same litter, only a week later. now the first gerbil is being violently chased by the new one, and shes being forced to stay on the top level where there is no bedding, only a hard platform, while the new gerbil is taking over the bottom half of the cage. there is no blood, no loose fur, no squeaking and they havent "boxed" or gotten into a ball and fought. do they just need time, should i separate them temporarily or wait until something serious happens? as of now, i made a temporary bed out of a box with bedding in it and put it on the top level so they are separated but have access to eachother.