At the end of Aliens, Ripley stows away in the pod with the young girl, and goes into stasis. In Alien 3, we discover that there was actually a face-hugger on board. Ripley later finds out that she's got a parasite inside of her.
However, her stasis pod was intact when she was discovered, and she was never attacked by a face-hugger in Alien 3. She also shows no signs of ever have being latched onto by a face-hugger; all previous attacks caused distinctive lacerations and abrasions to the sides of the victims' faces.
When / where did she get that parasite from?