So, let me start off by saying... HOLY RECOVER. She will let you get her Pokemon down to low health, then use recover. REPEATEDLY.
If you chose Bulbasaur, you should train it to level 20 and use a poison powder/leech seed combo. After infecting Staryu, switch out so you're healthy for Starmie. You will also most likely need a Pidgeotto to finish her off with speed. Otherwise, welcome to Recover City.
You may have caught a second Pikachu in Viridian Forest. If so, a level 20+ should be good, along with a Butterfree, Pidgeotto, or Beedrill level 19+. I'm not positive about this, so you may want to go north and capture a grass type.
Grass Pokemon to the north ~ Coming Soon