It depends what start date they put on the visa.
She cannot travel until the 'valid from' date on the visa, so if they have honoured your Intended Travel Date and made the visa valid from that date, she will have to wait.
If not, and they have used an earlier date, she can travel earlier.
What travel date did you put on the application? You really want to put the earliest possible date she could travel, so that she doesn't end up in a situation where she's stuck waiting for the visa to start and can't travel.
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