Hi hun, sorry for your sisters loss, its a devastating experience. Has she tried monitoring her cm or cervix position? Also she could keep an eye on her basal body temp. I personally just watch out for ewcm, but I know some others on here do the cervix pos/bbt. If she googles the subjects, Im sure she will find lots of info. Tons of luck to her.
Hope your gorgeous little one is doing ok too. Take care xx