The chapter begins with Abraham being advanced in years and wishing for his son Isaac to have a wife. Abraham has his servant take an oath to go back to Abraham's home country to fetch a wife for Isaac. As he sends the servant, Abraham tells him, "But if the woman is not willing to follow you, then you will be free from this oath of mine; only you must not take my son back there" (Genesis 24:8, ESV). So we see that Abraham is concerned about the freedom of the wife the servant is to pick; she must be willing to return, otherwise the servant is released from his oath to find a wife for Isaac.
When the servant arrives, he prays:
"O Lord, God of my master Abraham, please grant me success today and show steadfast love to my master Abraham. Behold, I am standing by the spring of water, and the daughters of the men of the city are coming out to draw water. Let the young woman to whom I shall say, ‘Please let down your jar that I may drink,’ and who shall say, ‘Drink, and I will water your camels’—let her be the one whom you have appointed for your servant Isaac. By this I shall know that you have shown steadfast love to my master" (Genesis 24:12-14, ESV).So this is a very specific sign that the servant asks for. It is interesting in that while mere hospitality might have someone give a drink to a stranger, it is above and beyond the norm for someone to also water the animals. Therefore, what the servant requests is not likely to be the result of random behavior. And because of that, he takes confidence that if he finds such a woman then he has found God's choice for Isaac's wife.
And we read:
Before he had finished speaking, behold, Rebekah, who was born to Bethuel the son of Milcah, the wife of Nahor, Abraham's brother, came out with her water jar on her shoulder. The young woman was very attractive in appearance, a maiden whom no man had known. She went down to the spring and filled her jar and came up. Then the servant ran to meet her and said, “Please give me a little water to drink from your jar.” She said, “Drink, my lord.” And she quickly let down her jar upon her hand and gave him a drink. When she had finished giving him a drink, she said, “I will draw water for your camels also, until they have finished drinking” (Genesis 24:15-19, ESV).So even before the servant had finished speaking his unusual request for a sign, Rebekah appeared...and then proceeded to fulfill the very sign that the servant had asked. And as we continue, we find that Rebekah did become the wife of Isaac, and she would later become the mother of Jacob and Esau.
But consider again the sequence of events. The fact that Rebekah fulfilled a sign is only amazing because the request was something that was so unusual it would guarantee for the servant that God was guiding him in that choice. This means it is an extremely unlikely set of circumstances.
So how did this set of circumstances come about if we assume Libertarian Free Will (LFW)? No supernatural being told the servant what to pray--the text indicates that the request came from the servant. Likewise, Rebekah's behavior appears to have been her own. That is, nowhere does she say, "An angel told me to do this" and nowhere does she say that she was compelled by external forces to water the servant's camels too. The fact that the servant had to run up to her indicates she was not close enough to have heard his request
So how is it that the servant just happened to ask, without external influences that would override his LFW, for the exact thing that Rebekah would just happen to be doing, without external influences over her LFW? It doesn't make any sense.
What does make sense is that God was in control of all that would happen, including the servant coming up with the request and Rebekah doing the action. And because there is no aspect of compulsion being talked about, and because it is impossible for this event to have occurred on LFW grounds, the only possible explanation is that this event presupposes compatibilism.