Linked / Imogen Howson.

Enhanced descriptions from Syndetics:

When Elissa learns her telepathic twin is the subject of government experiments, the girls find themselves on the run with secrets worth killing for in this futuristic, romantic thriller.

Elissa used to have it all: looks, popularity, and a bright future. Now, all she has is nightmarish visions and unexplained bruises. Finally, she's promised a cure, and a surgery is scheduled. But on the eve of the procedure, she discovers the truth behind her visions: She's seeing the world through another girl's eyes. A world filled with pain and wires and weird machines. Elissa follows her visions, only to find a battered, broken girl on the run. A girl--Lin--who looks exactly like Elissa, down to the matching bruises. A twin she never knew existed.

Elissa helps Lin evade the government agents who are ruthlessly tracking her down, but they're struggling to avoid capture, and soon Elissa is forced to turn to the only person who can help: Cadan, her brother's infuriating, arrogant best friend, and new graduate of the SFI space flight academy. Cadan is their one chance at safety. But Lin is too valuable to let go, and Elissa has knowledge that is too dangerous. The government will stop at nothing to get them back.