It's always going to be a tricky topic with transgender women. Supplemental testosterone (steroids) is outlawed in the mens categories, and men have more testosterone than women, so women who used to be men are likely to have residual benefit from that extra testosterone. If a male athlete said "but I stopped taking steroids 2 years ago", that probably wouldn't fly, so I don't know how much the same logic should apply to transgender athletes. I know a big strategy is to steroid up in the off season when they're not drug testing and then retain that muscle mass during the testing season despite having stopped taking them.
Also depending on the sport (e.g. boxing and MMA), bone structure differences between men and women (e.g. wider shoulders) could provide a significant advantage that no amount of time is going to remove.
I think her logic that "I'm not the best in the world, so it's not an issue" isn't exactly the best. She could, in theory, just be a bad athlete who's being boosted by some male advantages to becoming a good athlete. Obviously elite athleticism takes more than just a Y chromosome.
In the end, we'll probably wind up with good data that shows how much /if at all this is an issue. However, it's hard to say anything concretely at the moment for every sport because the pool of transgender athletes is still really small.
Also if the IOC says competing is a human right, surely then they violated human rights by banning all the doped up Russians..