If you knew the birth name you can get a copy of the original birth certificate, however while it will have adopted written on it, it doesn't have the name of the adoptive parents
Is this your friend's own adoption? If yes she can access her own adoption file. If it is not is the person still living? If they are I thought Roots Chat had a no living person policy.
Your friend can also access her mother's adoption file, the law was changed to allow that a few years ago.Speak to the adoption services team of her local council in the first instance for advice on the process.
It might be worth contacting the adoptions department at the GRO and ask them how to access her file if you don't have any/much luck locally.There has been a recent change in the law for relatives of deceased adopteeshttps://www.gov.uk/government/news/relatives-of-adopted-adults-now-able-to-trace-family-treeDawn