ctrob has good suggestions.
Notaries here are somewhat of a joke. Someone takes the document to the notary and the notary puts their stamp on it for all the signatures with no verification.
That aside, I have never given money for anything before I got the notarized copy and double-checked it to make sure it was still the same document with no changes. That includes my rental contracts which we renew every year because the landlord insists on putting the stupid 10% increase in there and every year I insist on not paying it so we have to start a whole new contract.
Bottom line, I wouldn't pay anything until I had the notarized copy. Not saying the landlord is being dishonest, but I tend not to trust anyone (not just here but anywhere) and this is too easy to get done the right way where your sister-in-law won't be in jeopardy of losing the money.