I think need only Teleport and Heal!
Teleport - it's important to be mobility.

Heal - improve your Heal in teamfgiths!
but there i think Heal can be change to Clarity, but only if your team need it.

Aura give to you and your team 6/8/10/12/14 (AP and AD)
So this spell can damage 2 targets at once!!! with 7 (4.2) sec of CD!
But this spell non-target. When you stay at line, 90% chance when you used this spel and enemy cham was in range, he will receive damage. In teamfights 2 target receive damage!! =))
Aura give to you and your team 8/11/14/17/20 (Armor and MR)
Heal spell non-target have 1100 range, heal champ with most few HP level.
Use this spell to defend your ally or yourself, more 20 armor or 20 MR can safe your life.
Aura give 8/11/14/17/20 movement speed.
Activation give burst of speed with some %. This spell give speed not only for ally but to MINIONS TOO!!!!! good tower rush! Use this spell when you need run away from enemy or rush them.At last ulty...
Deals 150/250/350 Damage and enemy dancing 1.5 sec ( like a Stun XD )
Use this spell when you feel that your enemy can escape over the battle and you or your team can kill him. Never start battle with this spell!!! It must be used as counterattack enemy or as Kill him with no chance to escape!

Hear all very simple.More mana, more mana regen = more casts in battle.
Just used it! I use only this Boots for her.
Give to you some Health and to you and your ally bonus Armor, MR and some Attack Damage =)
Give it to you More HEALTH! and to you and your ally CD reduction and Mana regen!
this item improve your mana regen and AP to your spells.
Armor and MResists , so if enemy focus you and kill you reborn to life with 750 Health and some Mana. great XD.

as 6 Item you can take whatever you want.

Marks you can change for whatever you want, because i dont know what can be more usefull.
Quits choose whatever you want to improve too =)
Seals and Glyphs can't be changed!

Let's see...

Bonuses for your team:
Armor = 32
MR = 35
AD = 22
AP = 14
Speed = 20
CD = 15%
MP/5 = 12
i think it better than nothing.

What about Game early\mid\late :
If someone told you than Sona can take mid, just laugh at him. She CAN! it's hard, but she can. So what about early game, at line or mid at early game you need just farm and stay away from contacts with enemy, if you do it best, try some haras them with 1st spell and passive ( Power Chord )
At mid/Late game you need walk with your team and gang enemy or get fight 5vs5.
Try get Golem buff! It give yors spell 4.2 CD, so when you use 1 of auras, all auras get Global CD for 1 sec ( i think so ), then if you get Golem buff just spam q-w-e-q-w-e-q-w-e-q-w-e.... and so on... every 1-2 second.


-Good LUCK and ENJOY! -