The most she would have had before was Sarah's mtDNA, which is probably doing GOOD to be 99/1. No canon source ever established she used her own DNA before.
This also addresses a minor plothole: It never made sense that Laura would look like Sarah. Revealing that Sarah DID use her own genetic material when creating her does a lot to explain her appearance. Frankly it also makes sense; the genetic sample was damaged, and she went with a female because the X chromosome was LESS damaged. But there was still damage that would need to be repaired. Sarah was doing this off-books, so she likely wouldn't have been able to use whatever genetic material the Facility had on-hand to fill in the gaps. Therefore she used the only other material she would have access to: her own.