Why should you pay tax for gift?

Gift tax is for everything above 13000 a year. However, if you receive a gift of $450,000, you don't have to pay gift tax. All you need is to claim unified credit, the $450,000 would be tax free, but your mother's estate tax cap of 5 mil would be reduced by $450,000.

I think your estate lawyer should have told you this. Other than that, I don't really know why you have to pay tax if your mother gift you the house.