There are narrations in Shia books which tell to fold the hands (for women).
As far as I'm aware, it doesn't say they should fold the hands, rather it says they should place them over their breasts (for modesty). Of course, nobody really follows that anymore, but even if they did, it isn't the same as crossing one arm over the other like the Sunni do.
Tadlees?
It's sort of hard to explain and hopefully one of the more knowledgeable brothers can explain it better, but I'll give it a shot.
Tadlees is when there is a discrepancy between the isnad and the actual real chain that occurred, with one or more narrators being left out but without the blank spot being noted. It's sort of similar to mursal (has a gap in the chain) but not really the same. Maybe an example will help explain it better.
Narrated A who heard from B who reported that he heard C say that his father, D, said that Muhammad (s.a.w) said such and such.
Narrated A who heard from B from C that his father, D, said that Muhammad (s.a.w) said such and such.
See the part that says "B from C"? It isn't explicit that B heard from the mouth of C. For all we know, B could have heard someone else say that C said such and such. And this other person that B heard from might be a fabricator. Hence, tadlees.
In that particular hadeeth, Aisha doesn't say how she came to know of the event. Did she witness it? Did someone tell her? It is unknown.