The event, at Thoresby Park, in Ollerton, north Nottinghamshire, also featured a 10km and a 10-mile route.
The autumnal trail runs involved running along old military roads, cleared tracks through ancient woodland and grassed paths around the country estate.
Willow was among the 74 finishers on the 5km route, running superbly for her young age to finish 17th overall and fourth female in the open age group, in 29min 25secs.
The overall winner was Jamie Boot in 20.06, and first female open age finisher was Amber Wilkins in 26.20.
* The 35th running of the popular Worksop Halloween Half-Marathon featured three Mablethorpe RC runners among the 2,421 finishers.
Roger Blake finished 896th in 1hr 51min 40secs, while Debbie Kew and Selina Elson made their Worksop debut and supported each other all the way round. Debbie finished 2,129th in 2hr 25min 06secs, and Selina finished 2,130th in 2.25.07.
Veteran runner Vivienne Martin, from Sutton-On-Sea, ran as an unaffiliated runner with hundreds of race miles to her name.
This was also her first time at Worksop, and she finished 1,587th in 2.04.01.
Stuart Spencer (Notts AC) won for the third year running in a staggering time of 1.10.05.
First female back was Natalie Burns (Lincoln Wellington AC), 27th overall in an impressive time of 1.20.47.
* Mablethorpe RC meets at Mablethorpe Athletics Club on Sherwood Fields, in Mablethorpe, at 6.30pm every Monday and Thursday. Everyone with an interest in running is welcome.
For more details, visit the club’s website at www.mablethorperunningclub.org.uk