See a real estate atty and have the atty draw it up , If she currently permits you to drive a vehicle over her property you want to have it spelled out that it is ingress and egress for the purpose of maintaining your property, I say it that way because since you only need it to maintain your property you dont want it open ended to be any kind of use other wise it may well scare away buyers of her property in the future , by limiting the reason it shows your not going have a 4wheeler party every other weekend using her land to access a party on yours . You could even have it written that it will expire when you sell your property so that way any new buyer in the next few years will know it wont last for ever.