Landlords wanting to put horses on property...

Ok question! We rent 2 acres. There's a big field on the property and the landlords told us they have someone interested in putting horses in the field. I said yeah absolutely, does that mean we have a slightly reduced rent? She said "it would result in an adjustment to the property maintenance portion or the lease so you wouldn't be responsible for mowing the lawn".

So basically she's going to double dip on the property. She's charging me X amount for the full 2 acres and charging this new person X amount to house their 2 horses without adjusting my rent at all. And my rent is not cheap in any sense. Its quite exoensive. What do I do here?