My daughter has the game Sun and Moon, she just got the game X and Y, she is trying to transfer her pokemon from Sun/Moon over with the bank-transfer app but when she goes to move them over it tells her she is unable to move that character, any suggestions please?? Thank you!
Unfortunately that is not possible.
You can transfer Pokémon from X/Y/OR/AS to Pokémon Sun/Moon through the Pokébank and you can put Pokémon from Sun/Moon on the Pokébank.
Unfortunately, any Pokémon that has been in a Sun or Moon game cannot be transferred to a 6th generation game (Omega Ruby, Alpha Sapphire, X or Y) even if it is the game it originally came from
It's unfortunate but avoids a lot of potential compatibility problems.
This answer to a similar question has the official picture detailing Pokébank capabilities for all the versions starting with the DS games. You should have a look if ever you wish to buy an older game.
It is possible so long as it has no new data, meaning that as long as it hasn't got any moves, ribbons or any other marking not possible in X/Y/or/as it is entirely possible to re-use it in gen 6. I've even done so for breeding sake since x/y was much quicker at getting the tedious stages of IV breeding done to then finish off on gen 7 for tournament legality