I think it is normal for your Mom to want to keep her memories with the folks that knew and loved your Dad. As for her question about the soul. I do believe that it is released from the body when physical death occurs.
This is a little strange and it was a very long time ago but I remember seeing something on TV about researchers trying to document this. They hypothisized that if the soul is real it must have some weight and therefore a dead body would weigh less than a live one. They got permission from from some individuals close to death to spend their last moments on a table that functioned as a finely calibrated scale. At the time of death they reported a very small, but measurable decrease in weight, which they determined was the soul leaving the body. At the time I thought this was as bogus as it gets and I remember the whole show as being creepy, but I couldn't stop watching it.
My belief, however, comes not from this show, but from my faith. I hope this didn't creep you out. If it did, I'm sorry. It just seemed that the question your mother was asking is one that many people have asked.