Yep use foam underlayment. However, the price they quoted you on it is outrageous. Not a single product I sell of this type runs more than $50.00 per 100sf roll at full retail. Be thankful she got the floating floor. You'd would've found out just how frustrating putting a nail is strandwoven bamboo without cracking it can be.
Don't know what part of the country you are in BUT strand bamboo does not do well in arid areas like the southwest. Pay particular attention to the relative humidity requirements that state for bamboo you must maintain 40% to 60% RH or your warranty is null and void. Also 2 to 3 year growth bamboo is crapt 5 to 6 year ok BUT Strand bamboo in arid areas i.e. low humidity on winter less than 30% or whatever the mfg states will and can produce problems. If you are in a humid area not so much.