Assuming it is just the sound and not the sight and/or motion of the vacuum cleaner that frightens your dog, you can help her overcome her fear by gradually habituating her to the sound. To do this you will need a realistic recording of vacuum cleaner sounds that you can play at home and control the volume of the sound.
There are many websites where you can purchase recordings of vacuum cleaner sounds as a CD or download (they are sold as white noise to soothe crying babies). Send an email to email@example.com and I will send you links to several of these websites. Test samples of the sounds at a loud volume to find one that your dog reacts to in the same way she reacts to your vacuum cleaner. Once you have a realistic recording, you are ready to start.
The process should take about a week or two. While you are habituating your dog to the vacuum cleaner sound, you should not run the real vacuum (you might want to do a thorough cleaning before starting this process). The next step is to find a volume level at which your dog notices the sound but does not react fearfully. This is your starting volume. Play the recorded vacuum cleaner sounds for at least several hours a day while your dog is in the house. Each day, turn the volume up slightly but not so much that it frightens your dog. Repeat the process until you can play the sound as loud as your real vacuum cleaner without any fearful reaction from your dog. If you use a music portable player, you can make the sound more realistic by playing it in different rooms. When you can play the recording at full volume with no reaction from your dog, start pretending to vacuum while the sound is playing. Next, run your vacuum while the recorded sound is playing, gradually reducing the volume of the recorded sound until the only sound is from your vacuum.
You can now vacuum your house without frightening your dog. No more excuses for dust bunnies!
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