It is highly unlikely that she is referring to Lavos when she makes the sperm metaphor, since she refers to the countless life forms already on the planet as the potential fertilizers. If Lavos were to fit into the metaphor at all, he would be a snake that eats eggs.
The speech is interesting, because it is hard to tell how literal the speech is. It is also interesting because after all that Serge and the rest of the Chrono crew did, NONE of them were named as the "one chosen life form which inseminates [the] planet." It merely said that Serge MIGHT be the one, at some point in the future. How much more legendary would this inseminator need to be?
