Solodice was part of a very awful experiment, where people from different walks of life were snatched up, had their brains removed, modified, and scrubbed of most memory, and then made to fight against each other. Solodice was the most successful of all of these, but in her final test fight against a combatant she was friends with, things hit a stalemate and was nearly killed.

She was set to be scrapped, but the two scientists who built her body hid her away, repaired her, and made a plan to destroy the testing facility and free the experiments. When a new arrival, a man named Morgan, was brought to the facility to be used as a new experiment, Solodice and the two rogue scientists stole him away. It turns out he was not sent to have his mind wiped, and was merely sent as a modified prisoner, shoved into a robot body through mental transfer rather than brain removal.
The four managed to sabotage the facility and escape, with Solodice joining the military force Morgan was part of.

However, the design details had been left behind, and so the company took what they had of Solodice spare parts, brain scans, and documents and created the Tetralin project. They were wildly successful, and became a mainstay among many armed forces.

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Soldier Bees are a product by a competing company opposite the tetralin project, which instead used a set of four brain mapping testbeds to create the entire product line. The four testbed units were sentient and free-willed, so it made working with them quite difficult at times.
Still, the final products were much more stable than Tetralins, and were often sought out for their multi-role versatility and product variation. This model is a space-use model, and was widely used amongst the interplanetary defense forces.
Even when Soldier Bees became very prominent, however, Tetralins were continuously produced at the same rate and were more reliable as a dedicated combat unit than most Soldier Bee models, whose multi-role modularity made them quite finnicky to bring up to comparative specs.
Solodice often found herself working alongside Soldier Bees, though often preferred the interesting conversation and free-thought among Tetralins, even if their origin made her feel awkward.