You must always have a vet check the sores first so the medical angle is covered first before looking to it being a bond issue. So please do have her seen.
We could not comment on the functionality of their relationship without a bit more information being provided.
How many piggies are there?
Are they all sows?
Their ages?
How long have they all been together?
How big is their cage?
What is happening/are you witnessing bullying?
If she is given a clean bill of health and you are finding there is likely problem in the relationship, then separating her with one of the piggies she does get on with and keeping them as a pair is likely the next step.
Bonds In Trouble
Sows: Behaviour and female health problems (including ovarian cysts)