If a girl is a Christian and she reads/prays according to Bible - is it permissible for a Muslim man to marry her?
Yes, it is permissible if she is chaste.
Allah has permitted Muslims to marry Jewish and Christian woman, on condition that they are chaste and avoid unlawful sexual relations. He says in the Qur'an (what means):
“Made lawful to you this day are At‑Tayyibaat [all kinds of Halaal
(lawful) foods, which Allaah has made lawful (meat of slaughtered
eatable animals, milk products, fats, vegetables and fruits)]. The
food (slaughtered cattle, eatable animals) of the people of the
Scripture (Jews and Christians) is lawful to you and yours is lawful
(Lawful to you in marriage) are chaste women from the
believers and chaste women from those who were given the Scripture
(Jews and Christians) before your time when you have given their due
Mahr (bridal-money given by the husband to his wife at the time of
marriage), desiring chastity (i.e. taking them in legal wedlock) not
committing illegal sexual intercourse, nor taking them as girlfriends.
And whosoever disbelieves in Faith, [i.e. in the Oneness of Allaah and
in all the other Articles of Faith i.e. His (Allaah’s) Angels, His
Holy Books, His Messengers, the Day of Resurrection and Al‑Qadar
(Divine Preordainments)], then fruitless is his work; and in the
Hereafter he will be among the losers”