Don't trust what others say about God's word. People are fallible. The best way to know for sure, is to study His word diligently.
It's kinda like what experts in counterfeiting do. When they're trained to know if a bill is real or fake they spend all their time examining real currency. They become so familiar with the real thing eventually they can immediately spot a fake bill from a mile away. It's really important in this day and age to be aware of the truth. There are a lot of lies being spread about Christianity these days.
Your relative is absolutely incorrect, and you have every right to stand firm in the truth, but don't be too hard on her. It would be easy to want to kinda rub it in her face, but we're children of God. We should do all things in love and concern, especially since she's likely not saved with those kinds of ideas.
If she's not interested in the truth, don't stress. You can't force the truth onto anyone. As long as you shared the truth. That's what matters. As Christians we plant seeds, and God gives the growth. It may take years for her to really come to know Him. God knows exactly how to get her there. Pray for her.
Here are scriptures in which clearly point to what Jesus did for the world (emphasis in red is mine):
John 1:19-34
19 And this is the testimony of John, when the Jews sent priests and Levites from Jerusalem to ask him, “Who are you?” 20 He confessed, and did not deny, but confessed, “I am not the Christ.” 21 And they asked him, “What then? Are you Elijah?” He said, “I am not.” “Are you the Prophet?” And he answered, “No.” 22 So they said to him, “Who are you? We need to give an answer to those who sent us. What do you say about yourself?” 23 He said, “I am the voice of one crying out in the wilderness, ‘Make straight[g] the way of the Lord,’ as the prophet Isaiah said.”
24 (Now they had been sent from the Pharisees.) 25 They asked him, “Then why are you baptizing, if you are neither the Christ, nor Elijah, nor the Prophet?” 26 John answered them, “I baptize with water, but among you stands one you do not know, 27 even he who comes after me, the strap of whose sandal I am not worthy to untie.” 28 These things took place in Bethany across the Jordan, where John was baptizing.
29 The next day he saw Jesus coming toward him, and said, “Behold, the Lamb of God, who takes away the sin of the world! 30 This is he of whom I said, ‘After me comes a man who ranks before me, because he was before me.’ 31 I myself did not know him, but for this purpose I came baptizing with water, that he might be revealed to Israel.” 32 And John bore witness: “I saw the Spirit descend from heaven like a dove, and it remained on him. 33 I myself did not know him, but he who sent me to baptize with water said to me, ‘He on whom you see the Spirit descend and remain, this is he who baptizes with the Holy Spirit.’ 34 And I have seen and have borne witness that this is the Son of God.”
Luke 5:30-32
30 And the Pharisees and their scribes grumbled at his disciples, saying, “Why do you eat and drink with tax collectors and sinners?” 31 And Jesus answered them, “Those who are well have no need of a physician, but those who are sick. 32 I have not come to call the righteous but sinners to repentance.”
Acts 2:36-38
36 Let all the house of Israel therefore know for certain that God has made him both Lord and Christ, this Jesus whom you crucified.”
37 Now when they heard this they were cut to the heart, and said to Peter and the rest of the apostles, “Brothers, what shall we do?” 38 And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit.
Luke 19:1-10
1 He entered Jericho and was passing through. 2 And behold, there was a man named Zacchaeus. He was a chief tax collector and was rich. 3 And he was seeking to see who Jesus was, but on account of the crowd he could not, because he was small in stature. 4 So he ran on ahead and climbed up into a sycamore tree to see him, for he was about to pass that way. 5 And when Jesus came to the place, he looked up and said to him, “Zacchaeus, hurry and come down, for I must stay at your house today.” 6 So he hurried and came down and received him joyfully. 7 And when they saw it, they all grumbled, “He has gone in to be the guest of a man who is a sinner.” 8 And Zacchaeus stood and said to the Lord, “Behold, Lord, the half of my goods I give to the poor. And if I have defrauded anyone of anything, I restore it fourfold.” 9 And Jesus said to him, “Today salvation has come to this house, since he also is a son of Abraham. 10 For the Son of Man came to seek and to save the lost.”
Don't forget the most widely known scripture:
John 3:16
16 “For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.
