She has a 6 year lease, unless that lease was written on the back of a piece of toilet paper by a drunk lawyer, then she should just quit worrying about things that might not, and probably won't, be a problem.
Just because the property is for sale, doesn't mean that things are going to change. Plenty of properties are bought and sold all the time with existing leases in place, it doesn't mean they are going to, or are able to, push you out, it means you get to change the bank account you are depositing your rent into.
I've never even met my commercial tenants, they were there when I acquired the property, and are still there today 6 years later, as long as the rent is in my account each month I'm a happy landlord.
Even if the property is sold to somebody who wants to redevelop, that doesn't mean they want or are even able to redevelop NOW, properties are commonly purchased and simply held for years, the new owners just sitting on the rental income until ducks are in a row, and that often means waiting for the existing leases to expire.
She has a lease, the purpose of a lease is to provide long term certainty, if it is not doing that, then that lease is terrible.