Black Widow usually escapes by taking advantage of her environment. If she's tied up in a room, she'll look for any sharp edges or objects that can cut the ropes. Sometimes, she'll play mind games with her captors. She might pretend to be weaker or more afraid than she really is, and when they let their guard down, she makes her move. Also, she has a great deal of knowledge about different types of restraints and how to break them. So, she can quickly assess the situation and find the best way to get free, whether it's by untying knots or breaking the bindings.
Well, in fanfiction, she may escape by using her charm. She could charm one of her captors into freeing her, either by flirting or appealing to their sense of honor. Another method is through her combat training. She can use her elbows, knees, or even her head to strike at her captors when they least expect it. And if she has any gadgets on her, like a small blade hidden in her suit or a device that can cut through the ropes, she'll use that. Plus, she's very good at reading body language, so she can anticipate the actions of her captors and use that to her advantage when escaping from being tied up.