Re: Gift Tax
Zion she would not qualify as a foster child as she is a connected party.
Nige is right, Favoured nephews/nieces only come into play where a going concern exists.
My recommendation would be to split the site into two agriculture sites (have your got a valuation on the site yet?) It's unlikely not possible that you may be able to obtain a low valuation for the land, €6,000 (unlikely, I know!!)
If you did get this sort of valuation split it in two, creating two gifts of €3,000 then get the uncle to gift the niece half and someone else half who in turns gifts that half to the niece.
This will result in stamp duty costs though....