I'm a bit late, but as far as how expensive the gift goes I would recommend asking your manager.

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Usually when people do secret santa, a rule is set in place of such as for example, "$20 max" so there's no situations where someone is spending like $100 and others are spending $10.

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Don't get too caught up on the price though, if you see some things that are nice and you think your co-worker Celine would like. You mentioned she likes coffee and cooking, maybe something like some cooking utensils such as a spatula for example or some good quality coffee if you know how she makes her coffee.

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Also general recommendation, whatever you do buy keep the receipt with it. Worst case scenario, if you buy her something that she doesn't need she can always return/refund it and get something she might need more. Most people care about the thought that goes into the gifts, so as long as you show you put some thought into it even if it's not kept don't feel bad!