The speaker has realized that nobody is coming to rescue them, and that they will have to do it themselves. The poem opens with a slightly wry "Guess I get to wear the shining armour now," which flips the old fairy-tale picture of a knight arriving to save someone. Here the speaker takes on both roles: the one in need and the one who steps in.
What stands out is how relaxed the speaker is about appearance. Armour, a t-shirt with jeans, an over-the-top gown: the list moves from heroic to ordinary to theatrical, and the speaker shrugs at all of them. The final line says the outfit "doesn't really matter," as long as the saving gets done.
The mood is quietly determined, with a touch of humor and maybe a little tiredness in that "Guess." It isn't a triumphant shout. It reads more like a calm, practical decision to take responsibility for one's own wellbeing, in whatever style feels right.