I'd certainly pay the mortgage off a.s.a.p.
However here are two links, to reputable sources of information, that might help your daughter to decide:
https://hoa.org.uk/advice/guides-for-homeowners/i-am-managing-2/pay-off-my-mortgage/
https://www.moneyhelper.org.uk/en/homes/buying-a-home/should-you-pay-off-your-mortgage-early#
NB (1): I strongly recommend that your daughter to ensure that she's got proof that she's paid the mortgage off. The Woolwich Building Society manage to mislay my final payment, of around £35k, and tried to repossess my house!
NB (2): Once the mortgage has been paid off, I suggest that your daughter should check the Land Registry's website to check whether or not the charge against the property has been lifted. About a decade after I got the Woolwich Building Society to accept that I'd paid off my mortgage, I tried to sell part of my garden to a neighbour, only to be told by a solicitor that I couldn't because there was still a charge registered against the property! (As the Woolwich Building Society no longer existed by that time, I had quite a struggle to get that error sorted out!)