Tenant with holding rent

My tenant is behind on her rent for a few months. Last week a brick was thrown through the window (she admitted by her ex boyfriend however there is no proof)
The window has been measured and we are waiting for the glass to be made so a new window can be fitted, which of course I had to sort out.
I reminded her about the unpaid rent and she said she will pay it when the window is replaced. So basically she is holding the money until the new window is fitted even though her rent payment are nothing to do with the window.
What should I do in this situation? ( the new glass is going to be 2 weeks and I’m sick of waiting and now she’s using the window as a means to hold rent)

Serve notice on the tenant