Hello and welcome. Thank you for providing us opportunity to help you.
Let me come straight to your question. IF you need to know how much capital gaix that your wife may incur if she sells her proprety for 300,000 would depend on many factors and you will have to work it out in the following manner.
1. To begin with, you will have to know your value of that property in 1983. That means, we need to know the basis -- the cost of that property to your wife.
2. You will add to that ALL the expenses (made solely for the purpose of increase .and / or preservation of value of the property to it.)
For exampla, if the market price of the property when your wife bought it in 1983 is 100,000 and she has made expenses of, say for example, 25,000 on it, then your cost basis for this property would be 100,000+25,000=125,000. If this sells for 300,000, then the gains on this property would be 300,000-125,000=175,000 -- Capital gains would be 28% of this amount of 175,000.
The following is a step-by-step guide to help you arrive at the capital gains calculation.
I am sure this would help. Please feel free to revert back with a reply if you need more assistance on this.