Even if she mated before capture and held on to the sperm? She was fairly big when we got her. The cave is really small and she blocks it most of the time but I still only see one and I would think they’d be clustered together. I was looking yesterday and couldn’t see it anymore. I don’t know if they can move them or would move them but she doesn’t come out ever.You won't see anything for several weeks, however, since you have had her for over 3 months, it is very unlikely that the eggs (unlikely there will only be one, the rest are likely deeper into the cave) will be fertile.
“The male octopus has a modified arm called the hectocotylus, which is about 3 feet (1 meter) long and holds rows of sperm. Depending on the species, he will either approach a receptive female and insert the arm into her oviduct or take off the arm and give it to her to store in her mantle for later. In the latter scenario, the female keeps the arm until she lays her eggs, at which time she takes the arm out and spreads the sperm over her eggs to fertilize them.” As you stated it’s most likely not the case but possible I guess?You won't see anything for several weeks, however, since you have had her for over 3 months, it is very unlikely that the eggs (unlikely there will only be one, the rest are likely deeper into the cave) will be fertile.
I did take a video and was able to capture the one egg that I have posted but she guards the cave or occupies most of the space as if she doesn’t want me to see inside or hides the egg(s). I don’t want to stick my hands in there because she actually swats at the algae magnet when I try to get her to reposition to see. She’s a feisty one and I’m sure she would defend and if not I don’t want to disturb her too much. I might try to draw her out a bit but from what I can see the one is not longer there...There are not too many (only one I know of) male octo species that actually give up their arms. Some, however, do give up their lives if the female is particularly hungry, ornery or just in a bad mood (we really don't know why some males are cannibalized and others of the same species are not). Yes, the female stores the sperm in both cases but the expected viability of the sperm is only about 3 (4 at the most) months.
If she is guarding the cave there is likely a larger clutch inside. You might try taking a video and then enlarging it to see if the camera can pickup more than your eyes (I have often found this to be helpful).
Your first sign of viability on the eggs will be black dots in the eggs so it will be helpful to try to take photos every few days if you can get an angle that shows an egg. These will be the beginnings of eyes.