Hi
She is seeking cover/protection. Guinea pigs are small prey animals that don't like to be exposed to open spaces where they are much more exposed to predation; it is on a very deep, instinctive level. Your chest is a very open and exposed place. Your girl is obviously still running on her prey animal instincts.
Give her a little blanket to snuggle under and she will be able to relax sooner and gradually accpet petting if you just start with your hand resting close to her and then increasingly 'accidentally' brushing against her and touching her. It takes patience and persistence and quite a bit of time.
The majority of piggies do not particulary enjoy snuggle time and will never do so for 10-15 minutes if you heed their wishes when they want to go home.
Be aware that what you see on social media reflects entirely what humans want to see and not the reality. And that those snuggly piggies are at the end of a process and not at the beginning. Ask yourself: Who wants to see vidoes of all the wiggly piggies dashing for your hand, your neck, under your pullover or try to get away from you that make up the majority?
Arrival in a home from the perspective of pet shop guinea pigs
New Guinea Pigs: How to Best Manage Arrival and Settling In
New Owners' Essential Information and Practical Tips Starter Collection
Understanding Prey Animal Instincts, Guinea Pig Whispering and Cuddling Tips
