Q: My little sister forget the passcode and make her ipad disable and i connected it to the laptop and restored it but now the ipad neew i cloud email and she forgot it :( so what should i do ??

Are you still logged into the account anywhere so that you can look it up ? Or do you have any of the account's downloads in your computer's iTunes library so that you can do 'get-info' on them and see the id ? If not have you tried : If you forgot your Apple ID - Apple Support ?

If you still can't find it, and if you were the original purchaser of the iPad (i.e. it wasn’t bought used) then you could try going to an Apple Store (make a Genius Bar appointment if you do) or try contacting iTunes Support online (http://www.apple.com/support/itunes/contact/) and see if they can remove the iPad from the account - they are likely to want to see proof of ownership before they might help e.g. original receipt with the serial number on it

You will have to find and contact the person that you bought it from, nobody on these user forums (nor Apple) will be able to remove that person's account from the iPad