A sister made an oath to sacrifice 2 to 3 chickens when she will know that her friend pass the boarders of a city safe, now this person is safe and the sister can't sacrifice because she lives in UK, and is not allowed to do something like that. Can she feed people or someone to do it for her in another country?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. Whoever vows to obey Allah (SWT) then he/she must obey Him, as stated in the Hadith (saying) of the Prophet (peace be upon him) reported by Imam Muslim that the vow to slaughter an animal for Allah's sake is an act of obedience that has to be fulfilled. So your colleague must fulfill her vow and slaughter hens, and if she cannot do it in Britain, she has to ask someone to do it on behalf of her in another country. She must not resort to atonement unless she is unable to fulfill the vow. Thus if she vowed to slaughter hens and then she failed to do, then she may resort to atonement which is stated in Allah's Saying: ...for its expiation (a deliberate oath) feed ten Masâkin (poor persons), on a scale of the average of that with which you feed your own families; or clothe them; or manumit a slave. But whosoever cannot afford (that), then he should fast for three days...[5:89]. Allah knows best.