Need some advice/garden issues

Tenancy Types and Management

In the tenancy agreement I have said the established beautiful plants need to remain but can be pruned gently and have provided instructions for doing so. The tenant was a keen gardener so was happy with it. I have seen that my wisteria which has been a beautiful established plant has been cut back to a 3 foot stalk. Any suggestions on how to discuss this matter as it is in breach of the agreement. I know it is only a plant but there are quite a few other changes that have been done in the garden such as building a brick barbecue, removing some fencing, etc. She pays the rent but how many things do you ignore