Sometimes we use personification. We pretend something is alive for poetic effect. In your example nature is personified as a woman/mother. Death is personified as a (male) skeleton with a scythe.
These examples are poetic, so you might say "Death stalks the plague-ridden streets, his scythe sharpened." (poetic) but "Death was at 19:45. It was due to a heart attack" (not-poetic)
People might refer to cars or ships as she (ships very often personified like this, even in quite formal language)
Look at her! She's a Porche 911. She'll do 0-60 in under 5 seconds!
I name this ship the Enterprise. May God bless her and all that sail in her.
As a rule of thumb, when we personify things that are protective or beautiful we use "she". When we personify things that are a threat we use "he". When we don't personify we use "it".
As a learner, you should always use "it" unless you are making a very clear personification. Use "it" for both nature and death, unless you clearly mean "Mother nature" or "the skelton of death".