Keep an eye on how many empowered stacks she has. If she has 3, play safer as her next ability will be much stronger.
Once she hits level 6, expect her to either look for kills in lane or set up her Jungler for ganks. Her Ultimate R is a strong tool that offers her extra kill pressure.
Whenever she uses her W, she will be vulnerable to an all-in. It has a really long cooldown, so try to abuse it if possible.
Avoid team fighting around major objectives if Seraphine is nearby. Grouping closely together is going to benefit her and allow her to get a good Ultimate R off and CC your whole team.
Similarly, avoid fighting in the jungle as your team will be grouped together which can allow her to get another good Ultimate R off. Try to fight in the open and split slightly apart so she cannot CC your whole team.
Seraphine will often go to ward alone during the mid-game. You can use this to your advantage to fight and pick her off. While she’s dead, you can look to take the Baron, a Dragon or look for a team fight with the numbers advantage.
At level 6, Seraphine will unlock her Ultimate R. This makes her more of a threat and she’ll be able to set up her Jungler quite easily.
Seraphine is good in team fights thanks to her Ultimate R. Avoid grouping closely together so she is unable to get a strong Ultimate R off.
Once Seraphine has completed her first item, her Q damage will increase and so will her kill threat. Make sure you avoid getting hit by her Q’s.