As I was reading your post I thought they may have come from B & Q before I got to that part. Some of the tiles they're churning out are absolute crap.
Onto your problem. If it is that bad then on the one hand I would be tempted to mention it to customer. At least then you could explain why the grout joints weren't perfect i.e. tiles are crap not
tiler. Problem is, on the other hand, the tiles are now stuck to the floor so she can't take them back for refund.
Difficult one. Are they really that bad? We are our own worst critics. Would they be ok with grout in? Sorry can't be any more help