Trying to understand her

I am trying to understand how she makes all these things work in her mind to not feel like total shit, or maybe she really doesn't have any conscience?

It is difficult to say what she really thinks, because I wouldn't know if the things she said were just in order to manipulate me or actually honest. For example she said she felt guilty after getting angry at me for no reason, but then she pretended to get angry and feel pressured by simple questions and tried to make me feel guilty and bad just to hide her activities.

She also said she was pissed at her french flatmate because he drank her lemonade. Would someone really be pissed for several months about something like that though? I think the real reason was that he was exactly like her and somehow it bothers her in others. In fact the smallest mistake of a peer seemed to piss her off sometimes, while her failings never matter or she couldn't remember them. This was how she reacted during the breakup fight as well. I made a small mistake during a BREAKUP so nothing she had done mattered anymore. She said: I don't care. and made the little mistake I had done in that moment the only thing of relevance. Maybe that's how she rationalizes? Taking a little mistake blowing it up in her mind and then brushing of her own actually grave misdeeds with that.

I also have to say at this point I think she is a notorious liar. She even lied in cases where it didn't really make sense. I saw her receive an SMS from her flatmate and she lied it was one of mine that arrived late. She lied about not having data connection on the phone. She lied about her working hours and time available.(and later she told me she never has time during the week, when I knew she was meeting another guy during the week) She lies when asking for information, she uses fake identities(she seems infatuated with her own name. It's usually María something, for example María Izquierdo.)
She also tends to lie that everything is fine to people.

Then she was insanely jealous and controlling. I was forbidden to do language exchange, she did it with another guy. I was forbidden to meet any new girl, she happily met new guys, saying they were old friends (when funnily in the beginning she told me having guys as friends is impossible).
So she didn't even allow me to do the same things she did, saying I would end up cheating(while she is a regular cheater and I never cheated). That's so sick I can't even begin to understand how she can look into the mirror. All this even after I offered her an open relationship. Why? The amount of guys she goes through in a short time frame is just staggering and the she says she is busy because of 'work'.

Somehow she seems to feel the world owes her(probably rooted in all her insecurities and problems) and she can do whatever it takes to get anything.
Sometimes however it seemed as though she did feel a little remorse when I said things which really hit home(not during the fight, but before).

She did change a bit (all my efforts in trying to get her better did pay off a little) she was a lot more stressed and easier to anger when I first met her. So all my suffering was not for naught, it did help her(although it got a little worse again during her time in France). She leeced me and threw me away when she had drawn all the blood she could :/