Flower Mound Farm Trainers

Siobhan O'Brien

Operations Manager and Trainer


Siobhan O'Brien is a United States Eventing Association ICP certified trainer with over 12 years’ experience training beginners through competitive riders. The ICP program certifies a trainer’s skill in dressage, show jumping and cross country. Siobhan has competed through the Intermediate level in Eventing including several FEI One-Star competitions.  She has brought numerous horses up the levels and enjoys developing both the horse and rider. She has had a lifetime love of horses but wasn’t able to seriously immerse herself into riding until she was an adult. As Malcom Gladwell writes in Outliers, it takes 10,000 hours to become expert at something.  In obsessive fashion, Siobhan put in her 10,000 hours and now derives pleasure from bringing horses into the lives of others.  She has owned and managed a private boarding and training facility in Flower Mound since 2002, Horselife, Inc.  Siobhan trains and shows in the disciplines of dressage, show jumping and cross-country.  She works with children and adults to introduce them to riding or to advance their competitive skills. Siobhan feels pride in helping people achieve goals at all levels.  A 17-year resident of Flower Mound, Siobhan also has three children and a supportive husband.  She is a two time Area Chairperson for Area V Eventing and is on the Board of the Texas Horse Park Foundation.



Ariel Koster

Beginner to Intermediates

From an early age I have always wanted horses to be a part of my life.  At eight years old I begin riding lessons at a local English hunter barn and continued through high school.  I participated in the United States Pony Club which furthered my knowledge of horsemanship greatly.  I even earned a National Championship in the Quiz Competition in 2003.  My passion for the sport continued to grow as I became a more serious competitor in the hunter jumper ring. My parents bought me my first horse at age 15 – my “Answered Prayer”.  Dante was my off-the-track thoroughbred dream horse that taught me a great deal, and carried me through many horseshow experiences.  Not just competing and winning blue ribbons, but he also taught me about myself and life-lessons through our rough patches together.
I attended college at Texas A&M and found a way to work horses into my degree. By declaring my emphasis area in Equine Studies, I was able to take riding classes such as Stock Horse where I rode western and learned reining, cutting cows, and trail patterns. Another hands-on class was Behavior and Training where I was assigned my own “un-broken” youngster and was able to train and ride him by the end of the semester.  My curiosity for other disciplines of riding led me to join the university’s Polo Club, which was a blast to learn such a revered and classic style of riding.
Since college, I wanted to expand my knowledge and experience with horses even more.  I spent a year and a half in South Carolina, where, as a working student and Assistant Trainer at multiple riding and training facilities, I received hands-on experience with training horses and barn management.  My love for Texas eventually brought me back home, and I now continue to stay active in the horse community here. 



Bridget M. Bello-Alcoba

Bridget started riding at the age of 9 when she began taking western equitation lessons in upstate New York.  When she was 12 years old, her parents bought her a horse and she quickly learned how much she enjoyed horse ownership and competing in local shows across New York and Long Island.

Bridget spent her college years riding for the LIU CW Post Equestrian Team and continued to compete as an Alumni member of the team for 5 years after graduation. During graduate school at LIU, she was invited to help with their equestrian team and had the opportunity to gain invaluable experience helping to prepare the beginner and intermediate riders for competition.   

She is also a NY State certified teacher and spent 15 years in the classroom where she worked with 3 to 7-year-old children.  Bridget and her family recently moved to Lantana, TX in November of 2014.

Bridget began riding at Flower Mound Farm soon after she moved to TX and was invited to help with lessons there soon after.  Her specialty is working with children and adults who have never ridden before.  Her patience and knowledge of child development helps her understand how to best motivate young riders and her fun and friendly personality instantly puts adult riders at ease and a smiles on their faces!


Mary Mahler

Mary has over 25 years of professional experience working with horses and riders of all breeds and disciplines. She rode saddle seat in her early youth and then went on to compete in hunter/jumper and eventing divisions. In her early 20s she discovered her passion for dressage and trained her first dressage horse, an Appaloosa, up the levels to Prix St. Georges to earn her USDF Bronze and Silver Medals. Her next mount, an Arabian, was also an unlikely dressage candidate. He started his dressage career with Mary at the age of 10 and was the IAHA Regional Champion at Prix St. Georges by the age of 14. Since those early days, Mary has trained a large variety of horses to numerous open and breed specific titles. She is currently competing her 13 year old Oldenburg gelding, Starrs and Stripes, at Intermediare I and her 6 year old Hanoverian gelding, Wrenegade, at 1st and 2nd Levels. Mary is very proud to have earned her USDF medals on horses she's started and trained up the levels herself, and she is currently half way to her Gold Medal with Starrs and Stripes.


7950 Cross Timbers Road, Flower Mound, Texas 75022 - 817.430.3182



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