We're moving... how to help her settle in?

My DH's gram passed away and now we're buying her house, but the catch is we have to keep her dog (an elderly Boston Terrier) and a 4 year old scaredy cat. Mitties has always been alone. Once when I was catsitting for a friend I brought the cat home and Mitties hated him so much she hid under the table for two days. Worried about her health, I brought the other cat home. She has never even seen a dog.

How do I introduce Mitties to these new residents so everyone gets along?

Feliway will be your holy grail.

Set Mitties up in a small room with food/water/LB/toys. I suggest sleeping with a bunch of blankets & putting those in her "new" room. Try to make it as much like home as possible for her, keep some things the same.

Give her time to adjust, then start the introduction process. Swapping blankets, etc.

As for introducing her to the dog, go slowly. Keep the dog leashed. Make a 'safe room' for Mitties by putting a baby gate up.