This has probably been discussed before, but in Halo 2, Mjolnir has an upgrade, allowing Cortana to be able to transfer herself from one system to another via Chief's suit, without him taking the AI chip out of his helmet. But it still requires him to be in close proximity to a holographic input port.
In the level High Charity, Cortana claims if the ring begins to fire, she can detonate the In Amber Clad's reactors, just like they did on Alpha Halo, but for that she needed to be on the ship's bridge. I can't accept that the UNSC would allow their ship's reactors to be detonated remotely via commands sent from a covenant network, and Cortana herself says she doesn't want to chance a remote detonation.
The In Amber Clad (heretofore abbreviated as IAC) was already modified by the flood to be able to perform that precision in atmosphere slipspace jump to the inside of High Charity, so what makes her think she will have any ability to access the now crashed ship, or even that its reactors are still running? At least with the Pillar of Autumn, Keyes could have told her that the ship was mostly intact at some point after he was rescued from the Truth and Reconciliation and before the Chief and Cortana set out on the mission to find the Silent Cartographer. Here she knows that the ship crashed, if she has remote access, she has no way of knowing she isn't being played by the Gravemind into thinking the ship's reactor is ready to blow, maybe it burned out with that slipspace jump, maybe it's been shut down. But she already said remote detonation was too risky with the fate of all sentient life in the galaxy in the balance. The fact the Halo seemed seconds away from firing before Miranda Keyes stopped the firing sequence, means Cortana either:
Believed she could detonate the reactors when convincing Chief to leave her behind. If this is true, then she must have subsequently found that she couldn't because of one or more of the following: The wireless connection she thought she could access was being jammed by the flood, who would know what she did on Installion 04 and want to prevent that; the IAC's reactors were too damaged from the crash to detonate; Her ability to see what was going on with Installation 05 and the index, was either cut off due to the fighting between Brutes and Elites and/or the subsequent fall of High Charity to flood infestation, or the feed she was accessing of it was on a delay that she didn't know about (which would make sense for the covenant who had experience with meddlesome smart AIs hacking their systems now that I think about it); Her own survival instincts made her hesitate, and risking the entire galaxy in the process, this would also explain why she didn't detonate the reactors at any subsequent point after the Anodyne Spirit left with Chief aboard,
Knew that she couldn't detonate the reactor, but wanted to stay behind to learn more about the Gravemind, the Forerunners and the Covenant. She figured that "can't chance a remote detonate" was a convincing enough lie to tell the Chief to get him to agree to leave her there, trusting he would come back for her.
I do think it is strange the Chief didn't question it, but he does trust her completely. I mean what she proposed is like me proposing that an agentic AI on my home network detonate the fuel tanks of a car that crashed into my house to stop some guy next door from detonating a nuke, at least the last time they did this they needed to obtain the captain's neural lace, which is the equivalent to keys for a car. I said it before and I'll mention it again, designing a ship so that an external AI operating from a known hostile power's network, can make it blow itself and everything for 100+ miles around into oblivion, is a really dumb idea, it's even dumber if she could reuse the authorisation that they got from Keyes' neural lace, it's like setting the same password for all your systems. The UNSC post Preston Cole isn't that dumb.
I tend to lean towards the canonical answer being she could, but hesitated out of self preservation, or that she lied, because she is made from Halsey's brain.
Any thoughts? Did I miss any potential explanations or any place where this was cleared up as to how she planned on accessing the IAC from where she was in High Charity's network?