Hi Theresa-Marie,
... la dernière fois que je t'ai vu(e). -- The last time I saw you.
Her the direct object (te) comes before the participle (vu, vue). In this case the participle needs to match the direct object in gender and number. Therefore, if the speaker is addressing a female, i.e., "te" refers to a female, the participle needs to be vue.
Same sentence, different direct object:
...la dernière fois que je les ai vus. -- The last time I saw them.
"Les" is masculine (or mixed gender) plural, which makes vu becume vus.
-- Chris (not a native speaker).
