Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
First of all we congratulate your wife for embracing Islam. Praise be to Allah who guided her to the straight path. We bring her the good news of the Prophet (Sallallahu Alaihi wa Sallam) brought to every new Muslim. Muslim reported in a sound Hadith that Amr Ibn Al As said: "When Allah instilled the love of Islam in my heart, I came to the Apostle (peace be upon him) and said: Stretch out your right hand so that I may pledge my allegiance to you. He stretched out his right hand. I withdrew my hand. He (the Holy Prophet) said: "What has happened to you, O' Amr?" I replied: I intend to lay down a condition. He asked: What condition do you intend to put forward? I said: I should be granted pardon. He (the Holy Prophet) observed: Are you not aware of the fact that Islam wipes out all the previous (misdeeds)? Verily migration wipes out all the previous (misdeeds) and verily the pilgrimage wipes out all the (previous) misdeeds.''
So these are glad tidings for all new Muslims that anyone who converts to Islam, all the sins he committed before becoming Muslim are forgiven. This is made explicit in the following verse, Allah Says (interpretation of meaning): {Say to those who have disbelieved, if they cease (from disbelief) their past will be forgiven.}[8:38].
Allah further says: {interpretation of meaning)''Except those who repent and believe (in Islamic monotheism), and do righteous deeds, for those Allah will change their sins into good deeds, and Allah is Oft-Forgiving, Most Merciful}.''[25:70]
As regards your question, the Fuqaha (Islamic jurisprudents) differ about the reading of Tashahud and the prayers upon the Prophet (Sallallahu Alaihi wa Sallam) while in prayer in language other than Arabic. Some of them say that it is permissible to say them in another language for whoever is unable to say them in Arabic, but it is not allowed for someone who can. Some other jurisprudents say that it is dislikeable to say them in another language for someone who is able to say them in Arabic, and it is permissible for whoever is not able to say them in Arabic.
Anyway, if your wife is able to say them in Arabic, then it is better and safer. If not, then there is no harm on her, Insha Allah to say them in English. With regard to the meaning of the prayers on the Prophet (Sallallahu Alaihi wa Sallam) you can explain them to her outside the prayer. We draw your attention to the fact that a Muslim should learn Arabic in order to understand the words of Allah and the Sunnah of His Prophet (Sallallahu Alaihi wa Sallam).
For instance, a Muslim has to learn what of the Arabic language suffices him to perform what Allah ordered or to say in the prayer and during the Adhkar (remembrance of Allah).
Imam Al-shafie said: "It is incumbent upon every Muslim to learn of the Arabic language what will enable him/her to perform his/her obligation."
If you meant by your question that both of you read (loudly) together and at the same time during the prayer, i.e. the husband reads and then his wife repeats after him, then this is not permissible. What is permissible is that everyone reads on his own. If she is unable to read, then she is excused from that obligation, but she has to learn that outside the prayer.
Allah knows best.