The first 3) things I'd like to know are 1) what is the TECHNICAL name for what your friend had installed? 2) What is the TECHNICAL name for what she WANTED to have installed? 3) Over what type of 'sub-floor' is this 'stuff' installed? (Concrete, floor joists 16" on-center?) Please state ALL the layers from the joists / concrete / whatever up to what was installed.
At first I thought your friend only had 3/4" tongue-and-groove sub-floor installed. Then you mentioned that the 'stuff' is 1/8th" deep. Aside from the fact that what was installed is NOT what your friend wanted, the specifications for what WAS installed required 1/4" gaps, and the 1/8" deep gap is the thickness down to the groove. So, before I advise otherwise, I need to know what is installed and what it's installed 'over top' of.
And further, is there any signed agreement for 'labor & material'? Please, if you're gonna give any disertation about a 'friend' did this for real cheap, well, unless you want your friends to keep being your friends, don't have them do work for ya'. (Just my unsolicited $.02.) I patiently await.