Laos is an easy country for women travellers, although it is necessary to be more culturally aware or sensitive than in many parts of neighbouring Thailand. Laos is very safe and violence against women travellers is extremely rare. Everyday incidents of sexual harassment may be more common than they were a few years ago, but they're still much less frequent than in virtually any other Asian country.
The relative lack of prostitution in Laos, as compared with Thailand, has benefits for women travellers. While a Thai woman who wants to preserve a 'proper' image often won't associate with foreign males for fear of being perceived as a prostitute, in Laos this is not the case. Hence a foreign woman seen drinking in a cafe or restaurant is not usually perceived as 'available' as she might be in Thailand. This in turn means that there are generally fewer problems with uninvited male solicitations.
It's highly unusual for most Lao women to wear singlet tops or very short skirts or shorts. So when travellers do, people tend to stare. If you're planning on bathing in a village or river, a sarong is essential.
Traditionally women didn't sit on the roofs of riverboats, because this was believed to bring bad luck. These days most captains aren't so concerned, but if you are asked to get off the roof while men are not, this is why.