Hopefully this won't be an issue. If the biometric has flagged then they will do additional checks to ensure she is not in breach of any immigration laws. However from what you state this should not be the case. Once they confirm this they can release her. Unfortunately, biometric failure is not uncommon. If possible you should provide the immigration with any of her documentation you have, if they still have her detained in the morning or they advise she will need to go in front of a judge you can look at getting a solicitor to come and help. Unfortunately until they investigate the matter and come to a determination they have the right to hold her. You could try speeding up the process by speaking with immigration to see if you can provide them with anything to help with confirmation of this. However, at the moment although a mistake has been made, they are simply following process.
I shall provide you with a helpful link that will assist you in finding a solicitor/representative near your local area. This will provide you with someone nearby your area who can assist you if required.
I hope this information proved helpful. You will find a local solicitor who deals with these matters on the law society webpage which is as follows;
https://solicitors.lawsociety.org.uk/ (England)
https://www.lawscot.org.uk/find-a-solicitor/ (Scotland)
https://www.lawsociety.ie/Find-a-Solicitor/Solicitor-Firm-Search/ (Ireland)
https://www.lawsoc-ni.org/solicitors (N. Ireland)
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