You are right. Since she has seen the patient before, they would be established. There is a good article on the AAFP website that explains it for them (though CMS has the info out there too):
It is from 2003, so be sure to make sure most still applies but it still seems to be current.
From that article:
When you change practices
Consider this scenario: Suppose you leave the practice where you have been working for a number of years to join a new group in a nearby community. Some of your patients transfer their care to the new practice and see you within three years of their last visits. You would report these encounters using an established patient code because, although you are practicing in a new group, you have provided professional services to the patient during the last three years. Note that whether the patient has transferred his or her medical records to your office and how long you may have had those records is irrelevant. The amount of time thatâ€™s passed since your last encounter with the patient is the determining factor.
There is also the decision tree in the E/M section of the CPT book.
Pam Tienter, CPC, COC, CPC-P, CCS-P, CPMA, CPC-I, AAPC Fellow
AHIMA Approved ICD-10-CM/PCS Trainer
AAPC National ICD-10-CM Trainer