I like Catriona, Tressa and Georgia best.
Callista calls to mind calluses and blisters, Elektra gives me an image of someone in a skin-tight satin catsuit with blue hair and the other two just don't appeal much.
Tressa has always been a very unusual name in the UK, but it has a long history of use, so it doesn't seem flimsy to me, just interesting. Have you considered Tessa?
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