This is the 16769th most frequent Russian word.
сложна
"Сложна" means "difficult" or "complicated."
Here, 'сложна' is used as a property adjective denoting 'complex'. It describes the nature of the task as demanding or intricate.
Эта задача слишком сложна для новичков.
This task is too complex for beginners.
In this sentence, 'сложна' characterizes 'life' as complicated, expressing the challenges and complexity in her situation.
Её жизнь сложна и полна трудностей.
Her life is complicated and full of difficulties.
'сложна' in this sentence is used in a hypothetical sense to imply that explaining the rule might be intricate or challenging.