If you take her on under PAYE, yes; you apply using a form P46, part of which they will have to assist you in completion. From what you indicate from you follow up question they will almost certainly be classified as an employee and must be paid within the PAYE envelope. Construction industry employees are an exception and MUST be paid under PAYE irrespective.
If self employed no. There is no need to employ an accountant if their affairs are simple. It is just one entry in the appropriate box of the self assessment tax return which HMRC automatically send out to self employed persons at the end of every tax year.
Here is HMRC's advice on UTRs;
'The Unique Taxpayer Reference (UTR) is only issued by HM Revenue & Customs (HMRC) when you, or your client, have registered for Self Assessment. It is made up of 10 numbers, for example(###) ###-#### ***** can be found on documentation issued by HMRC such as the Tax Return (SA100), a 'Notice to complete a Tax Return' (SA316) or a Statement of Account.
Depending on the type of document issued the reference may be printed next to the headings 'Tax Reference', 'UTR' or 'Official Use'. Please note: If you're self-employed and you register online for business taxes, you will automatically be enrolled for each HMRC Online Service that you selected. In all other cases, you'll need to register with HMRC for Self Assessment and enrol for the online service separately.
If you have not yet registered with HMRC for Self Assessment this must be done to get the reference before you enroll for the online service.'
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