Can my girlfriend sell her house that is brand new lived in under a year and avoid capital gains tax?

we have 2 houses and need to sell the newest one we are not married yet. Can the house that has been lived in under a year be sold and the money made be invested in my house so we avoid capital gains taxes and if so what are the ways this can work.Can they put capital gains tax on money that you put down on a house. The house she built she put 20000 dollars down on it and she will make 50000 thousand dollars so is only 30000 going to be taxed if she sells.Can we fix up my house with that 50000 thousand dollars and avoid capital gains taxes or do we need for her to put the 50000 dollars down on my mortgage. If we get married does anything change to make easier to avoid capital gains

i don't think there is any legal way to avoid capital gains, but i am not sure

You have to have lived in the house for at least 2 years as the prinicpal residence to avoid capital gains. As an individual you can make up to $125k or $250k married, and avoid capital gains ONLY if you lived there 2 years.

Yes, but there are exceptions such as relocating. Marriage may be one of those exceptions. I'd try IRS.gov.