Why shouldn't leona be able to cast her shield on an allied champion as well?

Give her some utility...? Strong initiation is nice but its not all that helpful when you're being ganked and the only way she can save you is by jumping on them and praying she'll survive as well (assuming one or both of you is extremely low.) Maybe as a passive buff for her ult? Ult > grant shield to near by allies as well or just be able to cast shield on allies