Your mollie might have ich, it just might be in her gills where you can't see it. Or she may just have a super strong immune system. Ich will die if it can't find a host, it will die at temperatures above 88 degrees, and it can't reproduce at temperatures above 86 degrees.
I think it takes about 10 days (might want to google that to get a more exact number) for ich to run its course and die if it doesn't find a host so I would think to determine if the water is safe for her fry would depend on how long it has been since the other fish died/when it first showed up in the tank.
How did you treat the ich outbreak? For me what worked was simply raising the temperature between 86-87 degrees. Three days after it disappeard I lowered the temperature back down to normal.
That's about all the information I have. I hope some of it helps you.