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.
Your wife has to do her best to get rid of the causes of fear. Driving fear away can be achieved by the following:
(1) Remembering Allah continually,
(2) Avoiding any misdeed,
(3) Supplicating Allah to help her,
(4) Seeking protection with Allah,
(5) Practicing Ruqyah (reciting some Quranic verses and supplications that are done by the Prophet).
This Ruqyah should include the recitation of Al-Faatiha (the opening Chapter of the Quran), Soorahs No. 113 and 114 from the Quran, verse 255 from Soorah al-Baqarah (Quran 2] and so on. At the same time, this Ruqyah is permitted to be done by another woman or by a husband, a father, etc. provided that it is limited to the Quran and Sunnah.
Your wife has also to show love to her husband since this is the best way to gain Allah's pleasure. The Prophet said: “A woman who performs the five daily prayers, fasts the month of Ramadan, keeps her chastity, and obeys her husband, will enter Paradise through any door she wishes.”
Also, your wife has to obey you (as her husband) when you ask her to bed since her obedience - Allah willing - will help both of you solve such a problem.
We also advise you to be patient and to take her to a doctor if needed.
By the way, if they cannot have sexual intercourse due to something related to you (as a husband), then she is allowed to bring the issue before the Sharee’ah courts.
Allah knows best.