Don't.
I am a fairly regular PayPal user, but would not use it for a vehicle sale, buyer or seller. I would agree to a deposit of some reasonable amount (10%, no more) and take the balance in some more reliable payment method. All of PayPal's Terms of Service are heavily in the buyer's favour. Dangerous in some cases as a seller.
Either she has the money in the bank, in which case she can easily come to some other arrangement, or she is financing via Credit Card.
If by CC, you can buy a payment doohickey for your smartphone to accept CC payments, in person transaction, and with a more reasonable fee than PayPal will charge you. They are inexpensive, sell them at Staples, etc.
However it does raise a potential fraud risk if the card she is using is not legit somehow. Like PayPal, resolution is pretty firmly in the buyer's favour.
I say decline or 10% PayPal and the balance in Certified Check when she takes delivery. Unless she can satisfy you with regard to why she wants to use these unconventional payment methods, it smells.