Honestly, this is a question that every person in Lithuania is speculating about.
Basically, the main theory is that she had good foundations built in Lithuania, but had some problems whilst training in UK. It is said that John Rudd made her develop too many muscles and she became too heavy, which in turn caused her to lose stamina and she was not able to go at her full speed as she constantly grew slower and her technique then suffered with every stroke. (she pretty much abandoned every other style she used to swim in during 2013-16, now she swims freestyle more often and is even trying 200m. breaststroke). Anyways, leading up to Rio, she had suffered from a huge injury, but her results started declining prior to that, so the injury was pretty much a good scapegoat from the lack luster performance in 2016. Of course, after that, everyone was confident there needed to be changes (a bit too late in my humble opinion), she got offers from all over the world, but for some reason she chose to come back to Lithuania and train in her hometown under a trainer, that does not have any experience with top athletes. Her results were very underwhelming the entire season, she participated in some low rank champs where she couldn't even finish 1st and had trouble holding back our second best breastroker. She also participated in our national champs, where she said that she was struggling with illness, missing some starts, participating in some until she was taken to the hospital on the 3rd and final day and there are no more news on her after that one.