forget apple id and password

See : If you forgot your Apple ID - Apple Support

To then reset its password : http://iforgot.apple.com

I recently updated my ipad to IOS 9.3 and its come up on the white screen where you have to type in your Apple ID and password.

I have completely forgotten the apple ID i used to set this Ipad up. It doesnt let me use any other accounts to sign in, I have also tried hard resetting it but it always come back to the same screen.

It says "This IPAD is currently linked to an apple ID, Sign in with the ID used to set up this IPAD", please someone help as its my little sisters IPAD and shes stressing out!

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 phone (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 phone 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

Forget apple id and password