Hi!
Please get her a same sex companion asap. Guinea pig are group animals and not wired to be on their own. She is feeling very, very lost and very alone without the protection of her family and friends. Keep in mind that pet shop piggies come from a commercial mass breeder and haven't had anything in the way of human contact.
Companionship is by far the best and most loving gift you can ever make her,
Companionship
Please read this link here to understand how a pet sale looks for a guinea pig:
Arrival in a home from the perspective of pet shop guinea pigs
Here are plenty of tips on what you can do. Please accept that we can't repeat them all in every single post:
How Do I Settle Shy New Guinea Pigs?
Understanding Prey Animal Instincts, Guinea Pig Whispering And Cuddling Tips
How To Pick Up And Weigh Your Guinea Pig Safely
What you should know when looking after single guinea pigs - they have their own social expectations from you just as much as you have your own human expectations from how your pet should be.
Single Guinea Pigs - Challenges and Responsibilities
Here is a list of the most common problems that owners of bought guinea pigs will encounter, including how your customer rights are handled in several countries:
New guinea pigs: Sexing, vet checks&customer rights, URI, ringworm and parasites
Here is our full new owners guide collection, which you may want to bookmark and use as a very helpful resource:
Wannabe and New Owners Information and Resources
It ranges from welfare compatible cage sizes, bedding; a good long term diet (can add 1-2 years to your guinea pig's life!), daily care; understanding behaviour; health monitoring and spotting illness early on; what to do in and emergency and saving up for vet care or where to get support from etc...