That means you are essentially selling it for $300,000.
If the Basis is $150,000, that means you will have a $150,000 taxable gain from the sale. How that $150,000 taxable gain will affect your tax return will depend on the rest of your circumstances (amount and kind of other income, which state you live in, which state the property is in, and much more).
You also referred to it as "investment" real estate. In the event it was rental property, some of that gain will be taxed at a higher rate due to the depreciation you were able to claim.
As was noted by others, you will need to file a Gift Tax return reporting the $300,000 gift.
Your daughter's Basis will be $300,000 so whenever she sells, she will have a large gain (hypothetically, if she sold it immediately for $600,000, she would have a $300,000 taxable gain). But if she is making that home her Principal Residence, that has special rules that could reduce (or possibly eliminate) the taxable gain if/when she sells.
