Vivian’s only way to do damage to you is her gun. When the ultimate is up, she’s really dangerous.
Her sentinels have AoE, and their size is kinda big, too.
Try to focus her sentinels when her ultimate is up, so she isn’t so bursty.
Maeve is a very good champ but you need to buy the right items: Haven or Blast Shield, Kill to Heal, Chronos, Cauterize are the best items. Only pick Wrecker if the enemy has a Torvald!