The established Sunnah is that a woman does not travel except accompanied by her husband or a mahram (a man she can never marry, such as her father, son or brother). The Prophet (peace be upon him) said, as narrated by Ibn 'Abbas and recorded by al-Bukhari and Muslim, "No woman should travel except with a mahram." A minority of later scholars permitted travel with a trustworthy group of women in conditions of complete safety, but the safest and majority position is to require a mahram, and this is the position to teach and act upon.
Evidence — the daleel
Sahih Muslim 1341 Ṣaḥīḥ
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.