I thought I understood this but as I look at it I can't quite untangle the grammatical relation between the words: I parse each word and offer a translation below. My real problem is the words 'partu' and 'ediderat' both of which can mean 'give birth'.
Silvia Vestalis caelestia semina partu
Vestal Silvia had borene divine children
ediderat , patruo regna tenente ...