All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
You should reassure your wife and tell her that she should not get worried and troubled as everything is in the Hands of Allah and whatever Allah has predestined will undoubtedly take place. She should be patient, get closer to Allah, seek His Forgiveness, abide by His Orders and supplicate Him. Indeed, Allah does not turn down the supplications of those who insist on Him.
Allah Says (what means):
• {And your Lord says, "Call upon Me; I will respond to you." Indeed, those who disdain My worship will enter Hell [rendered] contemptible.} [Quran 40:60]
• {And when My servants ask you, [O Muhammad], concerning Me - indeed I am near. I respond to the invocation of the supplicant when he calls upon Me. So let them respond to Me [by obedience] and believe in Me that they may be [rightly] guided.} [Quran 2:186]
Allah will respond to her invocations and give her satisfaction, Allah willing. In addition, she should know that the period you mentioned is very short and that not becoming pregnant in such a period should not be a cause for worry. Countless people have waited for years and years before getting children and at last Allah gave them what they desired.
As for continuing to read Surah Ya-Seen daily, it was not reported in a sound Hadeeth from the Prophet Muhammad . So, she should leave it and instead read whatever she can from the Quran as a whole, as the entire Quran is a blessing and a cure.
Allah knows best.