I don't have much Sheik team experience, but just looking at her moveset and playstyle, you can tell that she's a damage support character with decent disruption potential. I think the crux of her success in teams would be stage awareness. The more you have the more successful you will be, this is primarily always knowing where all three people are and what they are doing. Otherwise, recognize chances to disrupt an enemy's combo/string with a needle or a fast attack if your partner is getting screwed. idk how team synergy works, I would guess someone that is good offstage ie MK to help Sheik when she is offstage?