seperation anxiety

Mia had this for 2 years i say was this long as this was the time it took me to a: realise what the problem was b: solving the problem. So things i done to combat this

Got her at first to sit in a room with the door open i stood at the door and reassured her for a minute then built it up.
I then got to the stage i closed the door with mia in the room waited five seconds built it up again till she could stay in a room for 15 minutes, i would monitor her closely, i chatted to her constantly. I put her in a room she couldn't harm herself and put the radio on in the room for her i replaced my voice with music. Then i done this till every room in the house was covered . Was theree anything i could have done differently? Just i noticed a few seperation anxiety posts and wonder if my pointers/tips may help people.

ty ian xxxx