What are you feeding your rats? Sometimes they do this when they need better nutrition (but she's the only one doing this, right?) or they're getting too old to breed/nurse (but she only had 2 litters- that's not a long "career" at all) & unfortunately, sometimes they're just not cut out to be parents. What are the temperatures they're being kept at? Rats reproduction typically falls off in the winter (when it's colder), but in all likelihood, she's never going to be a good producer. No real way to fix this, especially since it's not like she doesn't know how to take care of babies- she just doesn't want to. Sometimes rodents kill & eat their first litter out of confusion- they get carried away cleaning up the afterbirth, & are hungry & just keep going-oops!When it's a first litter, mine get another "chance"; and if they only eat some & set some aside, not "cleaned up", I've found that if I clean them up & give them back, it suddenly clicks & they know what to do from then on. This one sounds like a feeder though.