Wouldn’t Mary’s flesh also be sinful? Wouldn’t that contaminate His being? The blood Jesus carried needed to be specifically human in order for the redemption to be effective; the body of Christ also needed to be specifically human in order for the redemption to be effective (Colossians 1:22). "Since therefore the children share in flesh and blood, he himself likewise partook of the same nature, that through death he might destroy him who has the power of death, that is, the devil, . . .Therefore he had to be made like his brethren in every respect . . . (see Hebrews 2:14-18; 4:15). Scripture does not seem to indicate that Christ was given “special blood” but on the contrary suggests that both the body and blood of Jesus was exactly like His brethren.
Christ specifically came as the second Adam to redeem the “Adamic” race (Romans 5:18-21; 1 Corinthians 15:20-22; Galatians 4:4, 5). That is why the Holy Spirit did not bring ‘special flesh’ or ‘special blood’ when Christ was conceived; Jesus is as human as can be. He has to be a true descendent of the royal bloodline of David (Romans 1:3; 9:5) in order to inherit the throne of His father (Matthew 1:17; Luke 1:27, 32, 69; John 7:42; Acts 2:29, 30). There is no hint in Scripture that God somehow took David’s blood and purified it before infusing it into Jesus at His conception.
The only reference that I can come up with in regards to mixing the holy with the unholy in regards to Jesus’ blood is in 1 Corinthians 11:27-30. It speaks of those that partake of His blood in the eucharist in an unworthy manner which leads to death. But your friend may think that Scripture is being too Catholic here!
The main confusion, in my opinion, that this person has is that she thinks that it is the body, and not the soul of an individual, that carries grace and sin.