"She wants to win by all means."
Translation:Sie will mit allen Mitteln gewinnen.
"mit allen Mitteln" doesn't sound unusual to me. (I'd suggest "at all costs" for "um jeden Preis", because if you want something "at all costs", it doesn't necessarily mean you're willing to use "alle Mittel".)
...but I'm wondering about the English sentence. Is that how a native speaker would say that "she wants to win and is willing to use all available means to achieve it"? Is it more like "She really wants to win badly" (like "unbedingt" in German)? Does it sound unusual altogether? Because I'm not sure I ever came across "by all means" outside contexts like "By all means continue destroying my possessions, I daresay I have too many", but... by all means correct me if I'm mistaken.
As a phrase standing alone, I would use the phrase "by all means" to mean something like: "most certainly" or "most assuredly". I would use the phrase "she wants to win by all means possible" to indicate that she 'wants to use all available means to win and to achieve it.' The word 'possible' it's not necessarily critical to the sentence, but I think it adds to the understanding of what one is saying.
Firstly, I'd suggest "at any cost" rather than "at all costs". Similarly, the given sentence sounds odd to me. Why would you want to use all means to win if you can win by only using some means? We'd be much more likely to say "She wants to win by any means." As in, she will do anything to win. Often "necessary" is also added to the end of the sentence.
sie will gewinnt,
Sie will gewinnen. gewinnt is wrong.
es egal wie ist
this part is needs to be es ist egal wie but you would rather hear 'Sie will gewinnen, egal wie!'. Your second part of your answer might be used in some cases to describe what the english sentence describes.
"gewiss" is a little bit old-fashioned, and it doesn't fit in here.
I think I'd translate "gewiss" as "surely / certainly" (which happens to be the literal translation as well): "My daughter is taking part in the competition." "Ah, sie will gewiss gewinnen / she surely wants to win? (This is what I expect your ever-confident daughter to do. / Am I right in assuming she wants to win?)" "Gewiss will sie gewinnen (of course she wants to win), but all the other competitors are stronger; sie wird gewiss verlieren. (She is certain to lose.) Ich bin mir gewiss, dass Anna gewinnen wird (I am certain that Anna will win)." "No, your daughter will win. Sie kann sich meiner Hilfe gewiss sein. (She can rely on me to help her)"