Well, in some fanfictions, Hermione has a hidden magical item. She might use this item to either teleport away or create a shield strong enough to hold off the Order members until help arrives. Maybe it's a charmed necklace or a special wand she had been saving for emergencies. Another way could be that she befriends one of the captors secretly and convinces them to let her go.
In this type of fanfiction scenario, Hermione could escape by using her knowledge of the Order's weaknesses. Since she is a very studious character, she might have known some secrets about the Order that she could use to her advantage. For instance, if the Order's hideout was protected by certain spells, she could reverse those spells. Also, she could try to communicate with her friends like Harry and Ron through a secret magical connection, and they could come to her rescue.
She might use her intelligence and magic skills. For example, she could create a distraction using a spell like 'Confundo' on her captors and then make a run for it. Hermione is known for her quick thinking, so she could also find a loophole in the security measures set by the Order.