You can, but why would you want to? If this agent is one you would be happy to have represent you, then give her all the time she needs. If she isn't such an agent, you shouldn't have submitted anything to her at all.
Far too many new writers worry so much about the time factor that they blow all their chances by submitting to too many agents before the query, or the novel, is actually ready. When an agent requests an R&R, then give her all the time she needs because she has already put time and effort into the novel, and she should be the one to benefit, if you did a good job.
All your eggs are not in one basket. You have all the time in the world to put your eggs in a different basket, if this one doesn't work out. Don't blow it. The fastest way to get an agent is not to submit to a lot of agents, it's to make sure you have everything as right as possible for the best possible agent.
And it is not a good thing to have an agent put in the time and trouble it takes to tell you she thinks need to be changed, only to have some other agent benefit from her work. This is not a nice thing to do.