Generally, women travellers will find that the Balkans is a safe and welcoming place to travel, whether you’re in a group, with a mate, or on your own.
That is not to say that sexual harassment does not exist, however. It is not unusual for women to be propositioned by strangers on the street, which can be annoying and even feel threatening, but rarely anything more. As a rule, foreigners are still a little exotic and therefore attract more attention, but this attention is rarely dangerous and is easily deflected with a shake of the head and a firm ‘no’. Do remember that in much of the Balkans a nod of the head means no, not yes, though! Use the local language if you can, but English usually works fine too.
In Muslim areas, women travelling solo will certainly be of interest or curiosity to both local men and women. In Albania, BiH, parts of Macedonia and southern Serbia, women may feel self-conscious in bars and cafes outside larger cities, which are usually populated only by men. Unmarried men rarely have contact with women outside their family unit and so may shower travelling women with too much attention. (In such areas, women travelling with a male companion will often experience the opposite and may need to pinch themselves as a reminder that yes, they actually exist.)
Unfortunately machismo still thrives in parts of the Mediterranean, where lewdness and harassment, though rarely dangerous, can become unsettling. If ignoring harassers, followed by progressively more forthright requests for them to bugger off, and truth or lies about your husband’s imminent arrival don’t work, then inform the police.
Whatever you do, don’t let these sad realities of an imperfect world deter you from getting out into it. On the whole, this is a welcoming region populated by salt-of-the earth, decent people.