Hello
If a person is in the UK illegally, they should try to get legal advice form a reputable firm of immigration solicitors to try to make an application to the Home Office in order to regularise their stay. In your sister's case, she has been here a number of years and had a child, so there may be an application she can make under the Human Rights Act, in particular Article 8 of the Act which concerns cases where it is considered that her removal would be a breach Article 8 of the ECHR on account of her family or private life in the UK. However, your sister needs to get advice quickly and if she has financial constraints, she can try to obtain the services of a legal aid immigration solicitor who may be able to take on her case at no cost to her.
The link below will also provide helpful information on where a person has been in in the UK illegally:
http://www.foreignersinuk.co.uk/guides- ... k_348.htmlRegards
Raheela Hussain
www.greenfieldssolicitors.com