Okay, thanks. Is the first of Leha's sentences the perfective form?
Yes.
Does that imply that when she likes me, she will have 'perfected liking me', ie she will always like me?
No. Perfective verbs don't imply something to be "going on", rather one-time action.
Would the imperfective form imply that she might change her mind?
Rather opposite: "Я буду любить ее всю свою жизнь" - полюбить won't fit here with всю свою жизнь.
I haven't got to learning that bit yet!
I don't quite understand this.