Eminent domain is required to be for a public USE, not "purpose". Clarence Thomas was crystal clear on this in his dissenting opinion.
Offering a "fair price" is immaterial. Property ownership means that the owner is supposed to have the right to keep or sell their property, except where the property must be taken for a public USE. Increasing the tax base is NOT a public use. If she held onto the property and later regretted it - that's HER fault. But she was not allowed to exercise her ownership discretion. She was forced to sell to a developer.
Look at it this way... I am willing to petition the government to give me your paycheck because I will pay them more in income taxes. They agree, because they get more money. We will give you an amount equal to what you are making RIGHT NOW for the rest of your career, even though it will cost me some money in the short term. But I get to pocket any raises you get, but you will have a guaranteed income equal to your current take-home (provided you keep working).
Would you take the deal?
An apt comparison.