Hey there,
being a mobile hairdresser myself I would love the opportunity to do my mobile on the side and work in a salon. I can't speak for your new staff but for me if i was ever given that chance i would jump at it, but for me i would respect that clients within the salon are strictly salon only and mobile is mobile. Myself I wouldn't tell clients in the salon i do home hair as this may jeopardise the business for my boos-you.
At the end of the day, if any of us have a opportunity to make a little extra outside of work we all would, you included no doubt
Also for me it would be that bit of independence on still holding a few of my own clients that I have control over. I would love to have this chance as I miss that salon atmosphere and the friendships with other staff....Maybe you should think of this with your new staff member, as I say it's just me, I would never dream of risking upsetting my boss by mixing home hair clients and salon clients, she may be thinking the exact same as me.
Maybe put it in her contract that she is not to disclose any information about her outside work. She isn't to speak of home clients in the hours of work, and as it already goes, no poaching (obviously)
But even if you have it in her contract to stop her outside work, she probably won't, I've worked with many stylists that do this, myself included, lots of us have our own clients outside the salon, I think it's just how it is.