I also wouldn't like someone else selling their own things in my shop / site. I would want everything to be about me, my skills, my products, my name.
I'm not sure how this would look in customers' eyes. Of course, you would have to state that, but how will you justify it?
What if you help her and then expects more down the line? Do you know what her plans are for her business? Is it a hobby or proper full time job? How will she turn things around to make her business successful?
I would perhaps hire her and pay her by the hour, but wouldn't take her work aboard on my site.