Basically it's whatever you agree to between the two of you. However without a sign model release you own the negatives [or whatever] but can do little with them. Get a copy of: ASMP Professional Business Practices in Photography 6th Ed. [may be a 7th out] isbn 1-58115-197-7 and good luck. As long as you two agree and it's in writing, tho it's pretty rare for the model to sell photos unless that's what you contract to do for her.