Interesting question ninXeno426!
It's one of those lines of dialogue that passes you by until you actually stop and question it.
I had a look around, and Scifi.stackexchange forum had a discussion on how they cloned ripley that appear to have the answer.
Just past some interesting points about the 2 paths of cloning they Auriga team used to get the clones is a comment that in the novelisation for Resurrection is apparently a line stating
"the film's official novelisation offers some additional detail. Her blood and various tissue samples had been kept on ice in the Fiorina infirmary when she had her initial physical (after being found in the escape pod). Those samples were cultivated and found to contain Xenomorph DNA along with Ripley's own. "