At some point before the events of "We Are Family, Part 2", Alvin captured Groundsplitter and caged her alongside other dragons on Outcast Island. With the help of Mildew, Alvin managed to trick Hiccup into revealing his dragon training secrets. Afterward, Alvin tamed her along with Mildew in the Outcast Training Arena.
At some point after being trained, Groundsplitter found a mate and laid several eggs, one of which was a large red egg that would later turn out to be the Screaming Death. The Outcasts placed crates of containing these eggs under Berk in an attempt to destroy the village. The offspring, including the Screaming Death, attacked the village in "Tunnel Vision", but were chased off by the Dragon Riders.
Groundsplitter remained on the island with three of her children until Hiccup and Alvin returned to the island and encountered her again. After talking to Mildew, Hiccup realized that Groundsplitter was the Screaming Death's mother and that it was destroying islands trying to find her. Alvin later releases her and her children during the fight with the Berserkers to bring him and Mildew into the battle and to fight the Berserkers directly.
Eventually, after receiving a Terror Mail from Hiccup, Fishlegs lead the Screaming Death to the island, which Groundsplitter immediately recognized as her child. However, upon realizing that the two knew each other, Dagur and some of his men captured her and threatened to kill her and allow the Screaming Death to destroy them all unless Hiccup handed over Toothless. Thankfully, Snotlout and Hookfang showed up and freed Groundsplitter. After Dagur was defeated, Groundsplitter and her offspring reunited with the Screaming Death and, after the Screaming Death gave a roar of thanks to Hiccup, they left Outcast Island together.
At some point afterward Groundsplitter and her family, including the Screaming Death, moved to Screaming Death Island, where they began to live. She encountered Hiccup and Snotlout, along with their dragons, again when she rescued them from the Screaming Death, who did not remember Hiccup and Snotlout. Remembering how they helped her and her family, Groundsplitter allowed them to take some of the Screaming Death's shed scales in order to make armor against the Dragon Hunters'arrows.
Groundsplitter looks very similar to a typical Whispering Death in the franchise.
In her debut, Groundsplitter has the typical personality of her kind; highly aggressive, violent, and dangerous. With these character traits, she seems to be a perfect match for Alvin, which allows her to bond with him.
However, she does have a maternal side, as she knew the Screaming Death was her offspring despite not being present when it hatched and was very happy to meet and be with her offspring.
She also seems to trust Hiccup and Toothless as they reunited her with her family and tried to help her when she was captured by Dagur, as she rescues them when the Screaming Death did not recognize them.
Alpha: Being the mother of her Family, Groundsplitter is shown to have complete control over them, including the Screaming Death.
Intelligence: She has shown to be able to remember her saviors from few years ago, as she was able to protect them from the Screaming Death.
Groundsplitter appears and was given her name in School of Dragons, where she is used as a rideable dragon during one of the Flight Club courses. Along with Stokehead, she is one of the only Flight Club dragons who's trainer is not identified.
Groundsplitter is the first dragon trained by Alvin & The Outcasts.
Like all dragons trained by the Outcasts, Groundsplitter was captured and caged to be trained.
According to Rise of Berk, Hiccup was close to training this dragon. When that happened is unknown, considering that the only Whispering Death Hiccup tried to train in the TV series was Toothless' Nemesis.
However, its possible that Groundsplitter is indeed the same dragon and was captured by Alvin some time off-screen, though this has yet to be confirmed.
Groundsplitter was speculated to be the Screaming Death's father.
However, according to the Rise of Berk developers, Groundsplitter is the Screaming Death's mother, which means that she is female and is the same Whispering Death that saved Hiccup from the Screaming Death in Dragons: Race to the Edge.