“Ukrainian opposition leader Yulia Tymoshenko slammed the plan, saying it would be illegitimate and unconstitutional.”
In 2010 after the presidential election, when she lost(45%) to Yanoukovich (48.5%), she refused to step down and recognize the result (verified by UE observers) of the election.
What is illegitimate and unconstitutional - is the deposition by violence of a leader legitimally and democratically elected.
He wasn't deposed violently. He just fled the country and the duly elected parliament voted unanimously to remove him from office.