This is the 17187th most frequent Russian word.
столкнулась
"Столкнулась" means "encountered" or "collided" (depending on context).
The word "столкнулась" is used in a metaphorical sense here to describe encountering or facing difficulties.
Она столкнулась с новой трудностью на работе.
She faced a new difficulty at work.
Here, "столкнулся" is used to describe a physical collision between two vehicles.
Автомобиль столкнулся с грузовиком на перекрестке.
The car collided with a truck at the intersection.
In this case, "столкнулись" is used to denote a chance encounter or meeting.