After having lived in France for over 20 years I can confirm Silvie is not a 'trendy' name there. Absolutely nothing wrong with it but it's a bit like being called Debbie or Lisa in the UK. It's very common among 50/70 year olds.
A bit like the current UK trend to call baby girls Elodie - in France it's as common as Laura or Emma or Lucie. I feel like in the UK people think Elody is a cool, alternative, unique, uncommon name. Just my experience.