Quick help any vets or Guinea pig familiar people!!!!!

[Beauregard]

I bought 2 female Guinea pigs on Saturday.
The one seems quite content and is happy to come out when we are around but is obviously still nervous but 'normally'so.The other is very timid and jumpy and has on about 4 occasions nipped the other one and sent her squealing.Other than this they seem ok but i do have concerns about the nervous one.I have called the petshop and they said that normally females get along and i can take her back today and choose another one.
I really don't know what to do,the nervous one rarely comes out of the little cave in the cage and when she does is so jumpy and scared.
I am worried that if she is nipping the other one so soon that it is a sign of more aggression to come.
Please advise me ,i feel guilty and sad for the nervous one but i have to consider the dd's and the other female guinea pig.
????

I used to be a veterinary nurse, and I've rescued guinea pigs for 15 years

Thankyou

They are still cagey around each other and the nervous one has nipped a few more times.

we have to male guineas (brothers) one is more nervous than the other and they have the occasional tussle but they always cuddle up together at night (aaahhh!)

she has nipped again ,someone has said to take them out and put talc on their fur to help them bond.

I suspect they might settle in a while - they have to get used to their new surroundings first I guess.