I find it very hard to believe that a professional roofer would change a minor cosmetic issue into a complete roof repair in order to scare a buyer off at the agent's behest because she was losing .5% commission. This makes absolutely no sense. You may need to take a second opinion on the roof to establish exactly what condition it's in, since that is what caused the original deal to fall through.
However, on the larger issue, of whether or not the buyer's agent is permitted to misrepresent any aspect of the property to the buyer, the answer is no, absolutely not. Having said that, don't forget that if two people are looking at the same glass of water, one might describe it as half empty and the other as half full and both be correct. It is the buying agent's job to highlight areas of concern with the inspection and negotiate a concession from the seller if one is requested by their client, the buyer. You may have been on the receiving end of a rather over zealous agent who made a little too much of it and scared the buyer off, but I wouldn't read too much into it. In any event, it's not something you are ever going to be able to prove, so my advise is to drop it and move one. More important, fix those minor repairs in the roof so it doesn't happen again!