If your wife received more than £10000 from a bare trust or an interest in possession trust, then a self assessment tax return is required, please see Check if you need to send a Self Assessment tax return
Your wife can regiser for self assessment here Register for Self Assessment
if she is not already registered for self assessment.
To send a tax return online with a trust section, will require the purchase of 3rd party commercial software. A list of software suppliers can be found here Self Assessment commercial software suppliers
If you send a paper tax return, all of the supplementary pages are available for download here Self Assessment tax return forms