Is it wise to ask a PhD supervisor about the quality of my work? She says, why do you want to hurry? Let's put the defense in December, then you can have several publications out till then. 

I am thinking of asking directly, "What do you think about my PhD work? Are you not happy with my work and is that the reason you are delaying correcting my manuscripts? "

Will that be appropriate? What should I do and tell/ask her?
Yes, it is appropriate to ask her what is going on. This is your PhD and she has no right to delay it in the way that she is currently doing. As a supervisor, she is supposed to support you in finishing your thesis, and if she is not doing that, you have a good reason to complain about it.

I do not think that it is even important what she is thinking of your work. If she thinks that your work is bad, that would make it even more important to give you this kind of feedback. So that is not a good reason to not give you feedback, and I also think it's highly unlikely that this is the actual reason why.

I would simply argue with the facts. After 5 years of doing your PhD, you want to be finished soon. In order to do that, you need her to give feedback on the manuscripts. If she says "why the hurry" again, there are several things you can point out, for example:


Postdoc positions usually start in autumn, so in order to get one of
those it would be good to have the PhD rather sooner than later,
since there is a lot of work to do for applications etc. beforehand.
You feel that you cannot use the additional time productively, since
you have done all the work that you wanted to do and do not need to
delay any further.


But actually, the question is beside the point, because it is your decision, not hers, and that is not why you are talking to her. If she really tries to derail the conversation in this way, I would call her out on it. "I feel like you are avoiding the actual issue I am addressing here. I have waited for your feedback for 1.5 years now. I think this is clearly too long, and now that I am ready to finish my PhD, I really need that feedback. I can understand that you are busy, but I have the feeling that you are frequently giving my work a low priority. I do not know why you are doing this, but it is frustrating. I currently do not feel appropriately supervised by you."

Well okay, I might have a slightly confrontational nature, so take this with a grain of salt. But I think in such a case it is adequate to criticize her for the lack of supervision that you have experienced throughout your PhD.

A last tip would be to give her deadlines. Usually people prioritize things where they get a clear deadline, even if the deadline is arbitrary. In the best case scenario, you can tie the deadline to an actual milestone of your final phase of the PhD - like maybe you want to say that by the end of March, you want to be done with the actual research and only focus on structure and design of the thesis, so that the deadline for her would be somewhere in March.