You must do such to be a Christian or your faith is of no worth.
Marry said let it be done unto me, now if she did not do as such, we would not of had Jesus now would we.
With faith comes actions.
Blind faith is a worthless act.
God could simply find someone else if she didn't. God could use anyone or anything if He needed to.
Luke 19:32-40 (KJV)
32 And they that were sent went their way, and found even as he had said unto them.
33 And as they were loosing the colt, the owners thereof said unto them, Why loose ye the colt?
34 And they said, The Lord hath need of him.
35 And they brought him to Jesus: and they cast their garments upon the colt, and they set Jesus thereon.
36 And as he went, they spread their clothes in the way.
37 And when he was come nigh, even now at the descent of the mount of Olives, the whole multitude of the disciples began to rejoice and praise God with a loud voice for all the mighty works that they had seen;
38 Saying, Blessed
be the King that cometh in the name of the Lord: peace in heaven, and glory in the highest.
39 And some of the Pharisees from among the multitude said unto him, Master, rebuke thy disciples.
40
And he answered and said unto them, I tell you that, if these should hold their peace, the stones would immediately cry out.
If God could raise up children of Abraham from stones, then He could also raise up a stone from the ground and use that to birth His Son.
Matthew 3:7-9 (KJV)
7 But when he saw many of the Pharisees and Sadducees come to his baptism, he said unto them, O generation of vipers, who hath warned you to flee from the wrath to come?
8 Bring forth therefore fruits meet for repentance:
9
And think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham.