They need a gun with a longer barrel and a higher caliber.
Changing any variable like that could change the outcome of the fight, and not necessarily in favor of the women.
A larger gun may have resulted in slower response & firing time, more misses and therefore possible injury or death to one or both women which did not happen with the guns they used which in hindsight, did not happen with the weapons they used.
Obviously they both could have died as it was but...
Statistically, the best gun for self-defense is a 9 mil. They have laser light attachments that give you one shot one kill ability at close range. A Glock weighing 2.1 pounds has been endorsed by Navy Seals. It has a short barrel.