If she had a partial hysterectomy, she might have only had one ovary removed, in which case she could do it. She might not have had her uterus removed.
You can't grow a baby outside a womb. Where would the baby get nourishment? Here's an explanation of what happens if an egg is fertilized and attaches outside the womb: it's essentially an emergency and could be fatal to the mother or would be aborted, it wouldn't become a baby: http://www.associatedcontent.com/article/364702/pregnancy_after_hysterectomy_can_i.html?cat=70.
This says very clearly, "Ectopic pregnancies cannot continue to birth (term). The developing cells must be removed to save the mother's life." http://www.nlm.nih.gov/medlineplus/ency/article/000895.htm
That said, if she's lying, it will become apparent in a few months when she isn't showing. Or you could offer to be supportive and go to the doctor's office with her: if she turns you down, she might be lying. Or you wait and see if a baby comes.
If your sister lies to this extent, she has a mental illness. You can treat her as someone who is ill and needs attention. You can also choose to see a counselor or minister about how you deal with her: maybe you shouldn't tell her personal things about yourself if this is how she reacts. Not to blame you or make you the victim, just something to consider.
And no, a baby attached to a liver would not be more stable. There's no way for the baby to get nourishment. If this was really happening, her doctor would be referring her to experts and she'd be visiting medical centers at universities and other doctors would be studying and monitoring her.
Is it possible she lied about the cervical cancer in the first place? Could she have had pre-cancer of the cervix, HPV, in which case they would have burned or frozen it off? Could she have lied about the partial hysterectomy? Like I said, offer to go with her to her next doctor's appointment.