2 teeth kind of turing gray why ?

It sounds like your mother is doing the right thing to talk to a dentist. Sometimes this is caused by trauma to the teeth (where the teeth die and the root cs turn black and stain the rest of the tooth). Usually the treatment for this is to have the root cs treated and then to bleach the teeth back to normal. This treatment is usually very successful, so I would not worry too much about it. Best wishes.