The essential theme of the movie is how changing the past to prevent something bad can work, but with the price of making other things bad. In the first episode of the TV series, Raimy learns this lesson, twice. She saves her father but her mother dies. And, just for good measure, she loses her fiance in the bargain.
Tonight's episode serves us another unwanted consequence. Raimy's mere investigation of the serial killer who murdered her mother in the new reality results in him moving away and out of Raimy's radar in 2016. The specific way this happens is neat, and a good example of how little differences can lead to big changes in time travel. Frank, urged on by Raimy from the future, goes to the home of the likely serial killer. The very visit sets in motion a series of events that get him to leave, which in turn leaves Raimy with no suspect at hand in the future.
And the lesson brings home to Raimy something she already knew: that anything she does to change the past to improve the future could also make things worse in the future, too. This puts Raimy in a difficult situation which makes for an appealing narrative: she has to weigh every single change she contemplates. Grasping completely the contradictory indications of any change in time, because she remembers all the original and changed timelines, makes Raimy (well played by Mad Men's Peyton List) the perfect time-traveled character - and she's not even traveling, just sending information from the future to her father in the past.
At this point, it's clear that the consequences of what Raimy is doing, and for that matter her actions in every episode, are unpredictable - or exactly what we want to see on television.
See also Frequency 1.1: Closely Spun Gem