Sister convincing herself she’s pregnant

This may be a sore subject but I need some advice! My sister lost her first baby in June of this year and says she can still to this day feel the baby moving (she was 6 weeks). Today she came to my house and asked me to buy her a pregnancy test even though she takes one every week and they have been negative she has convinced herself she is pregnant again. She has gone to doctors and gotten blood tests and one even did an ultrasound. I know how painful losing a child is, I just worry about her and want to help her.