I'm not an expert at this, ok. But based on my limited understanding of such matters, this is what your aunt needs to do, if she doesn't want to be disturbed while meditating.
Right at the start of her meditation, she needs to visualise a circle of white light around herself. (Or alternatively, a bubble of white light). The circle is protective in nature - within the circle, she's safe and secure and powerful. Nobody can come in without her consent.
At the end of the meditation, she should remember to disperse the circle. (Just visualise the circle. or bubble crumbling or dissolving or fading away, or whatever). Don't forget to disperse the circle. Don't leave these circles just lying around your home.
All this magickal circle stuff can get much more elaborate, but the simple steps I outlined above may be sufficient.
Here's an example of the more elaborate stuff: http://user.cyberlink.ch/~koenig/sun...wie/circle.jpg
Stonehenge, in the UK, was probably used as some kind of magick circle as well: http://naturalpatriot.org/wp-content...stonehenge.jpg