When she and Lee get back from the repair shop, she says she has something to do.
She decides to keep the battery just in case they mind leave without her. So, at the point she clearly intended to go with them…or hold them back for a while.
However, if in your game she survives, at the end, she leaves the house without notifying anybody, not even Lee who barely managed to catch her at the stairs.
Is she hiding something you think?