Hello BalkanGem,
I like about your guide on Sona that you‘re keeping the most important things, such as runes and items, as short as possible. However, if I may, I would like to suggest adding more champions to the threats and synergies roster. For example, Nautilus is also quite a problem for Sona while playing against Soraka should be fairly easy.
I would also add some game play information on how to play her, combos and such.
But these are mere suggestions. You‘re on the right track. :]

Cheers, Wicked Cherry.

9/12 games won with this build , IMO its solid for someone who almost never plays Sona.