Does Sona have to ready exactly 4 runes, or can she ready fewer if less than 4 are tapped?

Ruling: You ready as many runes as you can. If you have fewer than 4 runes exhausted, you ready all of them.

Nuances:

• The ability does not require exactly 4 runes to be exhausted to resolve
• You do as much of the effect as possible with what is available