If your friend's mother is able to make the application (or at least sign the forms) the £30 fee is waived.
There is apparently a large backlog of requests awaiting processing by the Disclosures team at Cranwell, so it will take many weeks to arrive
When you get the copy of the service record it will contain a lot of abbreviations and jargon - the Museum staff at Hendon (
[email protected]) have had a lot of practice in interpreting such records and should be able to help you/your friend understand the hieroglyphics.