So, Jasmin Paris and Nicky Spinks have each become outright holders of long-distance challenge records this year; but neither of them (to the best of my knowledge) has ever won a race outright, although Jasmin came 3rd at Wasdale in 2014. However, women have been doing well in recent FRA-listed races in the Deep South, with Annie Conway's 2nd place (by 9 seconds) at Exe to Axe in 2015 and Sarah Rollins's 2nd place at Surrey Hills (Long course) in the same year. And it is near the South Coast that the most famous (because it appears to have been the first) outright victory by a woman was recorded (though not in a FRA race): Sarah Rowell's win at the Beachy Head Marathon in 1986. According to the list at the bottom of http://www.arrs.net/TR_Mara2.htm , she seems to have started a trend of women winning off-road marathons (mostly in North America).
Victories by women in overseas ultra races also seem to be fairly common, and I know of Carolyn Hunter-Rowe's 1991 win at the Round Rotherham Run. But what about shorter fell races? I know of two outright victories by women: Carol Greenwood at Erringden Moor in 1998, and Katie Walshaw at Coiners in 2014 (what is it about the moors above Calderdale?). There was also a win by Sarah MacCormack at a road race in fell country, the Langdale 10k in 2014; this race was also unusual in that more than half the 624 competitors were female.
I have done a fair amount of rooting around in websites of foreign mountain races (not ultras), but the only examples of outright wins by women that I have come across were both in Alaska. There was Allie Ostrander's 2014 win in the very competitive Mount Marathon Junior Race (over 100 boys and over 100 girls). The other case is back in 1990, at The Bird Ridge race, a 3-mile uphill-only event with 3400 feet of climbing. In a field of 38 men and 10 women, Nancy Pease finished 94 seconds clear of the first man. Her times in 1992 and 1993 were even faster, but on both those occasions one man managed to beat her. And she is still going strong, having set a new W50 record on this course in 2015.
PS Is Carolyn Hunter-Rowe any relation to Joan Hunter Dunn http://www.poetseers.org/poets/john-betjeman/love-song/ ?