I'll take one last stab at this with the assumption your friend is after the exact model. But let's try it via a possibly different option.
If, this MBA is attached to an iCloud account, and if they can access that from another device eg iPhone they can try going to:
Settings>Apple ID (at the very top), scroll all the way down to see if that particular device is listed. Should this be the case, the following information could be available: Model, OS version and Serial Number.
Many "ifs" here but I'm just guessing from what little information is provided.