Positive test but not pregnant????

Is there a way for a woman to get a positive pregnancy test without out being pregnant? My mother is 43 years old and is supposed to be having a hysterectomy on the 14th. She is homeless and jobless. She lives with my husband and I right now. She says she hasn’t had sex since October (I don’t believe her on that) and she says she took a pregnancy test last night and it’s positive. She had to have an abortion 2 years ago of twins because if she didn’t the pregnancy would kill her. That’s what she told us at least. She hates herself for it, but the twins most likely were not making it out alive either way. I cannot support her if she is pregnant. It’s hard enough as it is with my husband, me, and her. The pregnancy would be high risk if she kept it, I just can’t do it. She has convinced herself that she has cancer in her uterus, but no doctor has confirmed it. I am kind of freaking out. She says she is sick all the time, extremely tired. She has had 3 periods since she has been here though she says. My mom has been known to lie. I just don’t know what to think or do.