OK,. I KNOW the easement setback is 25 feet.
So you have a copy of the easement - that's good.
Are you saying that she should be responsible for pruning the tree?
Depends on who is responsible for the maintenance of the ingress/egress easement. If you're responsible, she would retain timber rights to the tree, but little else. Be certain to research whether or not the tree is a protected species before engaging in further tree work.
The tree is in the middle of the easement.
Does this mean it's in the middle of the driveway? If possible, get together with the landowner and request that the easement be moved so the tree is no longer a problem.
I was told by the local fire department (who ordered me to intall the tank) that they could not access my property with a fire truck because of overhanging branches.
Now we're getting somewhere. Get that statement in writing from the fire dept. chief. This tree clearly presents a direct safety hazard. Talk to the owner regarding the movement of the easement. Tell her you either want the easement moved to a place where you will have the ability to receive deliveries and access for a firetruck should the need arise, or you will be removing the tree (if maintenance is in fact your responsibility).
Do this verbally first in order to be a good neighbor, then certified mail when you're ready to take action. Good luck.
I am not an attorney. I don't have an attorney. I don't even know an attorney. My advice should be given the same consideration as that of a 5 year old. In fact, you might just give that 5 year old the benefit of the doubt