I understand the concern but speaking as one who grew up in rattlesnake country, jeans and mid- to high-topped boots were always sufficient. Few snake bites occur to feet or legs when long pants are worn. The fangs just won't penetrate shoe leather or denim. The greater threat is to hands and arms when curious youngsters reach for something that catches their eye. Medium-high hiking shoes with long pants should be plenty of protection. Adding some form of hiking gaiters would make her almost invulnerable.