Your sister probably had more moths or beetles around to pollinate the blooms. This could just be sheer numbers or the nights yours were in bloom, the weather was not conducive to pollination. :-((((
If they are prickly, and there the plant I'm thinking of you have more than enough seeds to last.
Hope this helps.
Frank

Did you use fertilizer? If you did, yours got nice and green. While your sisters got flowers. They don't get the flowers if you use fertilizer just lushy green leaves.

I am going to assume that you are talking about Datura since you made reference to prickly seed pods. Datura is self fertile(doesn't require a pollinator), though they are often pollinated by hawk moths. Let me ask if you are deadheading your plant. If you remove the spent blooms, you will have no seed pods. Did your plant bloom well? You didn't say.