Not after a defeat, but after a defeat with the king dead and no immediate heir? Most likely Anora had her allies within Loghain's circle and if push came to shove they'd choose him. Loghain had control of Denerim he imprisoned the Arl, appointed his henchman, created a public enemy in the alienage, recruited guards on a massive scale all of that within days. I also didn't say that Anora was put under house arrest but that Loghain could have put her under house arrest any moment. Under those circumstances her movements were very restricted. Anora probably made Loghain regent so he could secure the throne for her, which he most likely intended anyways as the crown was always out of his reach.
Also if it weren't for the warden all the nobles would have been on Loghain's and Anora's side, even Eamon.
If Anora was so capable then she should have been able to take control of the situation even after a major defeat. Even with the king dead and with not heir. After all, Cailan was even more incompetent than Anora, and no great loss, and an heir is not so important as long as there are other strong leaders to rally around. The problem here was that Anora was not as strong as she thought she was, and because she had made no allies among the nobility they did not rally to her. Loghain may have had the support of his local lords. But he as a common born general could never hope to effectivly unite the nobles of Ferelden. If Anora had been a good ruler she ought to have had plenty of allies all around. Evidently she did not. Loghain only had one powerful ally, Howe. And Anora had none at all.
Again. Nobody had true control of Denerim. Howe had the arl imprisoned and was made arl himself. But aside from the palace district and fort Drakon the guards in the city was loyal to their officers and not him. Anora, the queen had not a single soldier loyal to her.
We've no evidence there was much recruitment in Denerim at all. In fact, all across Ferelden there was little of that at all. Anora's administration of the country was not strong enough for a draft to be effective. Especially after Ostagar. Instead Loghain seems to have relied on mercenaries to fill the ranks, hench his need for gold and the enslavement of elves (which Anora did not discover or stop, showing how little she had developed her networks in the five years she was the "de-facto" ruler).
Anora probably ran to Loghain because she was in over her head and wanted daddy's protection. Loghain, being the real power behind the throne had little trouble securing the support of Northern Ferelden through his Ally Howe, and the rest of the coast through the minor nobility under Gwaren. He and Anora proved very much incapable of gaining the loyality of the critical Bannorn and western Ferelden. A capable ruler would have been able to secure their support, and would have made allies among them during peacetime. Anora did not, and Loghain likely could not due to his common birth.
As for the nobles. The civil war should counter your point quite effectivly. Only the surviving nobles, and those able to reach Denerim will side with Loghain if the Warden is not present. The Civil war would have carried on, only now with Redcliff on Loghain's side. Loghain won himself some breathing room with a few victories. But without the Warden there to remove him it would have continued. Besides. The nobles will side with Loghian, and not Anora in any event. She has no allies personaly.