You're making a gift of property worth 80k. Because the property is land, you will need a solicitor to draw up the transfer instrument. The solicitor will advise on the tax liablity but, yes, your niece is likely to have a liablity to to gift tax, the exact amount of which depends on facts not given in your post. (There's a "favourite nephew/niece" relief that can avoid gift tax when the property transferred is business assets and the niece has been working in the business, but this is your house, so that relief is unlikely to be available to you.)
Stamp duty will also be payable.
As well drawing up and registering the transfer and advising on tax, the solicitor will explore whether there is any risk of the transfer being challenged by other members of the family (e.g. on the basis that your niece is being unfairly advantaged over other family members, and she has exerted undue influence over you to bring this about). You may think the idea is ridiculous or offensive, but solicitors are a pessimistic lot and they have seen too many family arrnagements of this kind end up in the courts when no-one initially expected that they ever would. So they'll want to go though the family situation with you, the reason for the gift and the context in which it is made, evaluate whether there's a risk here and, if there is, advise on strategies for reducing the risk.
There'll be the solicitor's professional fee to pay. Not negligible, but not likely to be as signficant as the tax liabilities.
All these taxes and costs, incidentally, are in principal matters for your niece rather than for you.