I wonder if your mom has ever collected anything? Most people have something they like to spend their "extra" money on. Some folks go on cruises, some collect antiques, some buy fancy clothing or Prada bags and $500 shoes. Some buy season tickets and attend every football game.
Everyone has things they spend their money on, passions they make time for. Ours is snakes(well and action figures for me too... ahem, but I digress...) and it's not a common passion/hobby. But then, Civil War re-enactors spend thousands of dollars, and several weekends a year with their hobby... some guys buy suits that cost thousands of dollars... some folks own $100K in jewelry.
It's all different strokes for different folks. Keep talking to your mom about your passion. Ask about her own hobbies or passions. Eventually she'll figure out it's not a "unhealthy obcession", it's a hobby.