Fiesty is
good Eating is
good You are right, those are some really
bad photos and I am glad you were not looking for an ID
From what I think I can tell from the arm thickness, this one may be fairly young. Be sure you have an inviting dark place in the temp tank. An artificial cave is fine. Mine seem to have preferred a slick bottom to a sandy one so an opaque plastic/glass jar might be ideal and would be something you can remove with her in it when it is time to put it in the larger aquarium. Try to make any escape routes undesirable, using lighting if needed but make sure a dark place is readily available.
There is some thought to keeping octos in a smaller enclosure for a couple of weeks to help them acclimate to humans better. I have never done it but have been tempted to try. With the given situation, you may as well experiment with the idea.
IMO: Do NOT put her in a tank that is showing ammonia. Amost anything would be better. DO go with your large water change idea and change water on both tanks often and DON'T use a chemical to try to correct the problem. On the temp tank, to keep the water safe, and on the existing one to get the environment stable. I would continue to use salted RO/DI in the temp tank since you don't really have a biological filter to help with organics that come in with the ocean water.
Fortunately, the spring is not the worst time for a drive to the shore, hopefully you will have a pretty day and can make the best of it (and double your normal water take). It takes me an hour + just to get to the airport to think about getting to the shore.
and they have gotten really picky about taking liquids on airplanes