My daughter and I bought adjoining land (she has one lot and I have one lot) and we may sell both for a gain of about 60K in profit each. How to avoid cap gains tax?

Sorry what you do with the money doesn't matter anymore .  You have a capital gain.  

To use the capital gain exclusion for a primary residence, you would have to build a house and live there for at least 2 years before you sold the property.  That's probably not what you had in mind.

If this is land you bought for business or investment, you might be able to do a "section 1031 exchange" to acquire a similar property for business or investment. Your gain is postponed until you sell the new property.  Section 1031 is tricky and most taxpayers need someone to help them arrange the exchange.  

Buying vacant land to build on and sell for a larger price indicates you intend to sell, not invest and doesn’t qualify for 1031 treatment. On the other hand, if you buy vacant land with the hope that the value of the land itself will increase, then you may be eligible to dispose of it using a 1031 exchange.

in a 1031 exchange, all the proceeds must go to buying replacement property that is also business or investment property (example: you can't use the money to buy a home for yourself) to completely avoid any gain. since these are separate lots if 1031 is available one of you may decide to do it and the other not. 

if this interests you and you haven't sold yet consult a tax or real estate pro for all the rules that must be followed. Fail on just one, and the entire gain becomes taxable even though you no longer have the money because it was reinvested. Also, know there can be substantial additional costs involved with doing an exchange vs just selling.