Silvia's gravestone does not exist within Veronaville, so she can't be made playable without the use of hacks and mods like SimPE. As a result, the only indication of Silvia's existence is provided by the family tree of her descendants. Strangely, Patrizio, Silvia's son has a memory of her dying shortly after Claudio, Silvia's grandson, married his wife, meaning Silvia would have died as an elder, which may explain why there is hidden picture of her in SimPE showing her as an elder with a different hairstyle, meaning that she may originally have meant to have died as an elder. This happens with many more Veronaville Sims.
This Sim has no character data and cannot be resurrected in-game. For more information, read this guide.