If a person has only ONE criminal conviction, which was over 11 years ago (and not within a specific group of offences, such as sexual ones), it's now automatically filtered from DBS checks. (A court has ruled that limiting the number of offences to just one is unjust but it's not clear if, or when, the legislation will actually be changed).
Further, since the 'filtering' system was introduced, employers should be modifying the wording on their application forms, to make it clear that 'filtered' convictions are regarded as 'protected' and thus do NOT need to be declared (even when the type of employment is otherwise exempted from the provisions of the Rehabilitation of Offenders Act 1974 [as amended]):
https://www.gov.uk/government/publications/dbs-filtering-guidance/dbs-filtering-guide
When non-spent convictions (for any type of employment) or non-spent ones (for those types of employment exempted from the provisions of the Rehabilitation of Offenders Act) are declared [or discovered via a DBS check], such convictions do not, in general,
automatically bar an applicant from the job. There are some specific rules (e.g. those set down by the Secretary of State for Education barring people with convictions relating to sexual offences against children from working in schools or by the Solicitors Regulatory Authority in relation to certain offences by solicitors) but, in general, it's entirely up to the discretion of the employer as to whether to regard a conviction as relevant or not.
So the childcare provider was NOT in any way obliged to refuse your wife the job and she most definitely is NOT automatically barred from working elsewhere in childcare. Further, if the drink-driving offence is her only conviction:
(a) it will no longer show up on a DBS check ; and
(b) she does NOT have to declare it on any job application, even when the application forms says that she should, because it's now 'protected'.