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The visa will be issued in two parts:
1) A visa vignette sticker in her passport valid for entry to the UK for 30 days
2) A BRP (Biometrics Residence Permit) ID card which she picks up from a designated UK Post Office within 10 days of arriving in the UK, which is valid for 33 months. This is her actual visa.
The 30-day validity of the visa vignette will be determined by the Intended Travel Date she puts on the online application. It will either be made valid from that date, or possibly from 7 days before that day, or if the date has passed before the visa is issued, it will be valid from approximately when the decision is made.
If she doesn't enter the UK within the 30 days, she will have to submit an application for a replacement vignette valid for another 30-day period to New York, which costs about £170 or so.
