Get everything in writing. Everything.
Spell it out bit by bit in the leasing contract and have both parties sign it. That way, there is no confusion and it is all in writing.
You can search the internet for sample horse lease agreements, but it is always a good idea to check your STATE law for any horse laws that may already be in place.
As far as what goes into the lease, well that's is completely up to you and them to decide. If she needs to call you before she comes out to the barn, put that in there. If you will be responsible for paying and making appointments with the farrier, put that in there. Put the due date for the lease payment in the contract and spell out what will happen if she doesn't pay on time.
You always like to think about the good in people, but it is just better to think about every possible "bad" scenario, and put the details in the contract. Better to have it in writing than end up in court over something silly.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.