Allah has power over everything and knowledge about everything. If he knows everything before, why did Allah create humans who are so worst in living creature, doing injustice, rape, trafficking, etc?
This is one of the major questions mostly every non-believer, even believers will ask and this is a great question that all Muslims should be able to answer with confidence. Whether the asker accepts the answer or not is up to them. I am in no way an Islam or Quran expert but I was asked this question many times by Atheists, Christians and Muslims and I will try to answer once more the best I can, hopefully it will give you some guidance.
The first requirement of belief is to accept. Not to make sense of it, but to accept. Whether you try to make sense of it or not is up to you, but there are references in Quran about using our minds and about reading/thinking, so, trying to make sense of it is definitely recommended but not to the extent to refute it if it doesn't make sense, as it will make you a non-believer.
While the perfect case will be to read, understand and make sense of everything in Quran, it is possible that no human may be able to make sense of some of the things in it till the Judgment day. What I mean is that when we read/learn something in Quran that doesn't make sense "to us", we still believe in it and accept it as the word of Allah and do not question it as we know that what we don't know, surely Allah knows. There are many verses about Allah knowing everything, but as an example, you can see Surah 76 - Verse 30.
So, In Islam, our belief is to accept that Allah is the creator of everything and Its existence comes from Itself (Surah 39 - Verse 62 and Surah 112). Allah created humans and jinn to worship It (Surah 51 - Verse 56). This means that we are created to be and live the way Allah wanted, not necessarily the way it makes sense to us or the way we want.
Once we accept that, it becomes easier to accept everything else in Quran and how Allah organized the universe, this world and this life.
In Islam, we also believe that there will be a Judgment day (Surah 78 - Verse 17). For a judgment to happen, there needs to be a test/trial and evaluation. That our life is nothing but a test, a preparation for the Judgment day and afterlife is mentioned in Quran in many verses (2:49, 2:155, 3:186, 7:168, 21:35, 29:2-3 and some others). Also check 29:64.
That humans are doing terrible things, that there is a lot of pain, hunger, suffering, injustice in this world is part of the test. If it was all-happy, all-perfect, there wouldn't be a test. Heaven is all-happy, all-perfect, and to earn it we must pass the test. Those who fail the test will most probably go to Hell. And once the judgment is done and everyone is distributed fairly (Surah 21 - Verse 47), nobody will claim there has been an injustice, not even a mother who lost her 3 kids in an accident, or a girl who was raped by a man for years or someone who has no sight or someone who spent his life with sins. Good or bad, everyone will realize the truth of Allah, admit their right or wrong doings and accept their fate.
One final comment about this question: While our lives and time is in flow for us from our past to our future, our perception of time and flow of universe is different than Allah's perception as It is who created it. My understanding from Quran (any verse that portrays the Judgment day) is that everything has already happened and the information about everything is logged by Allah. Allah's knowledge comes from that. But for us, we are still in the flow and we have no idea what comes next. We are given the free will and we become a good or bad person not because Allah knows it, but Allah knows it because we became a good or bad person at the end, it is just not finalized for us as we are still going through the test.
If a girl is raped or trafficked (as a part of his test), does Allah wants her to maintain endurance [As we know it is the biggest problem for women]? Why should Allah create human and want to play with our life? Is Allah sadist?
I believe my above answer also answers this question but to add a few things:
Allah tests us and wants us to endure, to show patience (2:45, 2:153, 3:15-17, 3:146 and many others), no matter how difficult it is (2:286), and reward us accordingly (9:72) if we pass the test. One should always remember that a harder thing can always happen to them no matter what situation they are in.
Allah didn't create humans or the universe to play with them (44:38-39 and 21:17).
Does Allah get satisfied after putting wrong-doer to hell? Instead, Allah should not have to create humans, Allah should be satisfied with Angel who are absolutely good.
When you are talking about The Creator, you don't say "should", that is, unless you are trying to "create" your own creator. As emphasized at the beginning of my answer, Allah does as It wants, not as Its creation wants or as Its creation thinks It should.
Allah doesn't want anyone to end in Hell, that's why It continuously sent prophets, books, warnings, lessons (3:108). It is humans who don't care where they will end, hence some of them will end in Hell and while probably all of them will regret for spending their lives non-believing and sinning (78:40), not any of them will think it is unjust. May Allah protect us all from Hell and the hardship of the Judgment day.
Brother or Sister, provide the answers (those who make sense to you) to your friend, but do not try to convince her as you can't, unless Allah wishes (6:111). Even the prophets didn't have the ability to convince people that didn't want to believe, not even their family members (Nuh's son, Ibrahim's father, Lut's wife, etc.).
There is the truth (Quran and everything in the universe that leads us to Allah), whether they accept it or not is up to them.
P.S. I didn't and won't include links to Surahs or Verses because it is up to the user to read Quran in whichever language and translation they want.