Which should I give my mum for Mother’s Day and which gift for her birthday?

I have a fine, white gold, white diamond pendant and a champagne and white diamond ring, that I bought from a secondhand store, still with their tags on. I’m poor, so I can’t afford new jewellery. My mum likes expensive stuff. Which is more appropriate; and for which occasion?

Updates
2 mo
I can’t ask my friends or relatives, as they’d be jealous or lecture me on being over generous.
Which should I give my mum for Mother’s Day and which gift for her birthday?
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