Need to Unlink my COC from my sister GC and link it to mine

i really neeed help. i play COC on bluestack with android then i got bored and link my coc on my sisters ipad because they say that it is easy to play on pad. i forgot to create my own GC and now i got one and i also buy my own ipad. but i cant unlinked or delete my COC on mysister GC. and i cant link my COC on my GC and i cant open my town hall on my ipad. i need help please!

Your backup is forever stuck on your sisters GC. Ask her nicely to make a new one and take over hers and use that to log in on your ipad. That is your only option.