The DVLA can revoke (or refuse to reinstate) the licence of anybody whom they believe may be medically unfit to drive. This, of course, includes those whom they suspect of being alcohol dependent.
She would only be a "high risk offender" if her conviction was on the basis of either (a) her recording more than 2.5 times the legal limit, (b) if she refused to provide a specimen or (c) if she had a second alcohol related offence within 10 years of the first.
The route to appeal this is via the Magistrates' Court. The DVLA should write to your friend giving her the reasons for the revocation, and whether and when she can reapply for her licence. If she wants to appeal this she must request a hearing in the Magistrates' Court. These are often tricky matters to challenge and, depending on the DVLA's reasoning, she may need to employ a specialist solicitor or barrister to put her case.
As above, there may be more to this than she is telling you because if she recorded twice the legal limit she would not be classified as a "High Risk Offender" and in normal circumstances the DVLA would not take any follow up action. Even if they did, I very much doubt that her saying "I had a few drinks over Christmas" would cause them to revoke her licence on that basis alone. In any case she must get the written confirmation of her revocation from the DVLA together with their reasons before she can proceed.