Whys my dog having separation anxiety ?

shes 5 years old and it just started happening. when my mom leaves she crys like really long ive never heard her cry like this before.. i dont know what this has to do with it but it started happening a week ago the dog was in a car accident but my mom wasnt even there. and she wasnt hurt or anything. but after that whenever she leaves the dog gets really upset and wont stop and shes gonna be gone for a whole week. whats going on?