I think a lot hinges on whether it's truly asking for help vs. telling you you need to do something, and possibly phrasing it as a question. Depending on how the organization is set up and the seniority of the person asking, it can be very hard for a low-level employee to say "No, I don't have time to do that."
Having multiple people that can give you contradictory orders about how to spend your time makes for a miserable job experience. You either work overtime to meet both sets of demands, or you get negative feedback from one of your "bosses" for not completing their tasks. It's the manager's job to prevent this, and it's important that they do so.
The correct response would be along the lines: 'Sorry, but you have to ask my boss if we can push it to the top of our task list as she has the overview over the priority queue'.
That is different than a 'No, I don't have time for that.', as it teaches how to do it right in the future, and your boss doesn't have to get furious because everything that happened was that the team informed the org about the regular process.
I have worked enough time in the midst of a QA team to know that planning is essential to their job. Nevertheless, a team lead which is going to be furious because you didn't use the correct process isn't someone you want to ask for help. So, in the long run, it might cause more problems than it solves.
That assumes that your manager has a reasonable process for prioritizing these kinds of requests, which is often half the battle. It also requires a manager that will go to bat for you and defend that process, even when the requester says "This is critical and time-sensitive, I don't have time for that, so can you just do it?"
Having multiple people that can give you contradictory orders about how to spend your time makes for a miserable job experience. You either work overtime to meet both sets of demands, or you get negative feedback from one of your "bosses" for not completing their tasks. It's the manager's job to prevent this, and it's important that they do so.