I checked this for my children and was directed to the following information, which I subsequently confirmed when submitting the application in person:
http://www.vfsglobal.com/India/UK/pdf/GuidelinesOCI.pdf
3. OCI registration certificate and visa have got to be re-issued by availing this service, each time a new passport is issued up to the completion of 20 years of age and once after completing 50 years of age in view of biological changes in face of the applicant.
Since your friend was over 50 when she acquired her OCI she does not need to request re-issue of her OCI against her new passport. I was also told there is no need to take your old passport with you. I can't remember the link confirming that info now.
Having said all that, one should remember that you're at the behest of Indian Civil servants here. I'm sure we all know why they sometimes choose to interpret the rules differently
As such, personally, I would take my old passport as well. Or have the OCI re-issued against the new passport. Reissuing is relatively cheap and "simple".