I'm not an expert, by any means.
I have given lead content a little thought as I have made jewelry for quite some time. Being prone to worry, I have always been careful about what jewelry I give to mothers of small kids. There can be both a choking hazard and one of lead leaching into their system if the baby or child put things in their mouths, like many are prone to do. A very sturdy sterling silver chain that the little one cannot break, or a fine silver medallion on a cord were favorites of mine.
I really wouldn't think that wearing a dress with crystals would be a hazard, but I wonder if there is anything more official in writing to ease your mind?
I share your thoughts that the glue, alone or in combination with the crystals, might not be too good for people. Probably worth keeping an eye on.
I live in California in the US, and anything that might contain a carcinogen or cause birth defects has a warning near it in the store. California's consumer labeling law is probably the reason Preciosa has lead free crystal now - this is only speculation on my part, though.
ETA see below for more information on Proposition 65, the law I referred to above.