She works fine there.
Start Q. W is strong as a first spell but you want your stun at level 2.
Max E first. The reason for this is that Q's mana cost goes up with level. E does not. This helps her as she requires two spells to stun. What you max 2nd is up to you. W has more slow, Q has more damage.
FQC, Sorc boots, Void Staff are your first 3 items. After that you can pick up what you want. This is, of course, after you finish sightstone.
- Deathcap for damage
- Ludens for poke
- Rylias for CC
- Liandry's for synergy with Rylais
- Athene/Morello for CDR(CDR scaling runes is also acceptable)
- Banner of Command for MR aura+ decent stats
- Hourglass
I'd say since you're support, always consider Ryalis. Follow up with Liandry vs health stackers or the team isn't building much MR. Otherwise Hourglass. Ludens is OK, but it's an item you want to get early for that 100 base damage power spike. It's not as amazing later in the game when you're more likely to get it. Deathcap is good too if you are not running into too much trouble with the enemy catching you, will overall provide you with the most damage after Void Staff.
Main problem you will face is mana sustain. As stated above, it takes her two spells to CC. Q's damage early on isn't all to impressive early either. So you can expect to need more mana to do good damage.
The next one is hard engage on you. With an easy to use knockback/stun combo you can easily defend your ADC. But you are the easier target. If they figure this out you may have a hard time.
Things you'll want to learn
- QE combo. This is your bread and butter as a support. It's mostly a thing of ranges and timing you need to learn. It's a fairly fast projectile so it's not too hard to land once you get the hang of it. And it's hard for the enemy to dodge for the same reason.
- When to R. Syndra's a high skill champ for the sole reason you require good positioning. Learning her basics isn't hard. But there's a lot of little things you have to keep track of outside of just cooldowns. Trying to R too soon will get you caught out and die. It's damage is high. Actually scaling harder on magic pen than AP.
- RE combo. More orbs for R is great. But you always get 3. This can turn into a quick AoE stun if you time it right and can easily turn a teamfight to your side. Remember you're not there for the damage.
- Orb stacking. This is overall, put down 2 Q's. Pick up the first Q with W. Then Q, W, E, R the enemy. This hits them with 6 orbs if you timed it right. Deals W's damage and stuns them at the same time. Getting this down will give you higher burst than most assassins. Killing them before the stun even ends. Keeping this in mind. Once you have the mana sustain try to always keep at least 1 Q down when near enemies.
- Mana management. Stated above. But you have to get used to this on her. Most of her power is form comboing her spells.
- Q/W+AA. Her Q and W have no cast time. Meaning you can move while using them without stopping. Much like Vel'Koz W. This means you can double tap your harass in lane. While most have to cast a spell to harass back you can do both then move. Her AA animation is good too.
- Landing your Q's. The radius isn't that large and it's not hard to dodge it. It's not too hard to get used to it. But once you do you overall can combo it with every attack you have. Landing a W followed by a Q at the same time does a good chuck of damage to make people fear you when you are holding something with W. Your Q cooldown is something you'll want to almost feel when it's up.
- Lane control with W. If your lane is pushing and you don't want it to. Pick up a minion and put it closer to your tower. You can do this on an even lane too. Just grab one early(although this is risky moving to their half) and throw it back to your side. Giving your side a larger safety net as you don't have to over extend as much to harass and setup possible ganks.