Ok, let’s get this turned right around right now!
I agree with
@BannerPenguin, you hold all the cards and you need to start thinking like a businesswoman and forget about trying to be friends.
As a business owner, you need people to respect you, not necessarily to like you. That’s an important distinction.
In this instance, the virus can work in your favour. Tell her what’s going to happen when you re-open, and that it’s not open to negotiation. Charge her a set daily rent payable for 52 weeks a year that gives you a fair profit. If she’s unwilling to accept the new terms, let her go.
In your shoes, I wouldn’t have her back anyway as she’s likely to be resentful of the change in the relationship dynamic.
I’d tell her that you’ll be re-opening alone when the time comes, then just before re-opening, advertise the chair for rent at a daily rate. Salons will have to operate with fewer staff and service fewer clients to allow for social distancing so there will be more clients looking around for appointments. That also means there will be self employed staff looking to pick up extra days in another salon, so you can choose to be picky about who you rent to. Find someone who is grateful for the opportunity to work in your lovely salon.