Yes, if you accept the risks and also understand that you may already have it from previous partners.
Two negative results in a row means she isn't infectious at this time, but it doesn't mean she may never be infectious some day. And assuming you two have negative STD results for things like Herpes, HIV, chlamydia, Hep C, etc. And assuming she is on birth control .And assuming you two are in a committed relationship. Ideally, unsafe sex is reserved when two people have been in a committed relationship for months. So my advice is to be really sure you two are committed to each other before having unsafe sex.