help me to correct grammar

Suggested changed are made below:

Thirst undermines the courage of (or you may say discourages) the besieged and the rulers of the Israelites contemplate surrender, but Judith, a widow, reproves them and says that she will deliver the city by her own plan, and then tells the rulers of the Israelites, "I am about to do something that will go down through all generations of our descendants."(8:32).

Then Judith (1) HAS herself dressed up, (2) MAKES up and (3) prays, “Give to me, a widow, the strong hand to do what I plan” (9:9). “Please, please, God of my father … hear my prayer! (9:12). Before Judith goes to the camp of their enemies, the ruler of Israelites prays,“May the God of our ancestors grant you favor and fulfill your plans” (10:8).

WITH BEAUTY (and irresistible charm), Judith goes into the camp easily. Then, Judith processes her plan, telling the general Holofernes what the situation the Israelites are having and how great King Nebuchadnezzar and Holofernes are, to be TRUSTED. By gaining Holofernes' trust, Judith is allowed TO access to his tent one night, takes advantage of Holofernes' intoxication and Judith prays, “Give me strength today, O Lord God of Israel!” (13:7). Then, Judith cuts off his head by striking (HIS NECK / THROAT ?) twice. Having lost their leader, the army of Nebuchadnezzar (incomplete sentence, you mean they are in chaos?) Judith SAVES ISRAEL WITH her (WISDOM, COURAGE, FAITH) and beauty.

all "Holofernes" are "Holoferne's"

The last 2 sentence "Having lost their leader, the army of Nebuchadnezzar"

consider revising