I've met a number of female touring cyclists, some solo and some not. Overall it comes across as a positive experience. You are indeed more vulnerable traveling by bicycle, however people are aware of that and act accordingly by offering greater hospitality and assistance. In some regions with more traditional attitudes it can still be dangerous and inadvisable, however in most of the US and many other countries you'd be fine.
Also, you can find people to ride with, for the short or long term, if you prefer greater comfort that way.
Safety understandably affects women as a concern more than men in riding in general (not just touring). I wonder what changes would help make women feel more comfortable touring?