Yeah as long as you have more than the subtracted amount she doesn't die (otherwise as long as she doesn't hit 0). I forgot to mention that you can only use the planeswalker abilities when you're able to cast a sorcery spell.
Planeswalkers can be attacked. When you declare attacking creatures, you choose whether each one is attacking your opponent or a planeswalker that opponent controls. Your opponent can block as normal, regardless of what each creature is attacking. If a creature deals combat damage to a planeswalker, that many loyalty counters are removed from it.
Other sources can deal damage to planeswalkers. If a spell or ability you control would deal damage to an opponent, you may have it deal that damage to a planeswalker that opponent controls instead. So while you can't target a planeswalker with a Shock, you can have a Shock that targets your opponent deal 2 damage to one of his or her planeswalkers instead of to the player. You can't split the damage from one source between a player and a planeswalker. Damage dealt to a planeswalker results in that many loyalty counters being removed from it.
The quote just uses shock as an example of a damaging spell that can target a player.
you can't use healing abilities the same way, like a heal targeting yourself and be applied to the planeswalker instead, can't be done. I could be wrong on this.