Another student has been assigned the same MSc thesis as mine (and already defended) I am in a dilemma as to how to approach this issue. Basically, myself and another student were assigned the same thesis topic. Only difference is, I have been doing it part time and she completed her in 2017. We both were liaised by the same co-superviser who has now left the university.

The whole thesis is the same. I do not just want to re-word her thesis, because I actually want to learn something. However at the same time, I have had a lot of busy months at work and because of that I have been lagging behind in my thesis. 

She did some simulations and produced some results and discussed it. My simulations are the same as well. So, it is Okay that I replicate the results using my own simulations (even though its the same)? Or do I have to do something completely new? The literature review part is going to be similar as the topic is similar. I personally think, there isn't much I can do differently besides explaining the same results in my own way.
The answer is very simple: ask your current supervisor and be completely transparent with them about the situation. Whatever is acceptable to them is the right answer. Standards for masters theses are much more flexible and inconsistent than for doctoral theses, so, for all practical intents and purposes, whatever your supervisor approves is acceptable. (But this assumes that you are absolutely transparent and do not withhold any information about the situation from them.) 

But be sure to email a recapitulation of their response to them and let them reply, confirming that you have understood their resolution correctly. That way, you have an official written record with dates so that there is no forgetfulness or confusion in the future. (In fact, that's a general tip for any important verbal conversation throughout your professional life.)