It doesn`t matter, whether I would give her the same wage already while hiring or in due course later on
Actually it does matter. Now that makes sense - you wouldn't immediately go up to her and offer the same wage as the $30 guy if she's already agreed to $25, instead you'd wait around to see if she's worth increasing her wage by $5 and not arbitrarily increase her wage a day after being hired just to match a man who managed to negotiate a higher salary. No one would say hey, I know the job posting said $25 an hour, and you agreed to it yesterday - but since there's a man we just hired today that's making $30 I'm going to give you the same as him.
I decide about wages and they will be equal regardless of gender coz I like it like that.
Except you just contradicted yourself by stating you would wait to find out if she is as good as the male worker, which makes total sense - no business person in their right mind would go up to a person and offer them a raise when they didn't ask for it just because a person of the other gender negotiated a higher salary.
In my 15+ years of working in businesses both large publicly traded ones, smaller businesses, and running our own family business I've never seen a female with the same title, same experience, same capabilities be paid a smaller salary than a man. And I sure as **** know that 99.9% of businesses in the USA and other developed countries like Poland are the same because if there was wage discrimination then they'd get sued.
If anything, the only wage/hiring discrimination that occurs is with seniors. Businesses often don't want to hire someone that's too old because well one they're old, they get sick more often, probably won't be there for a long time, and don't have the same mental and physical capabilities as a younger person. And if they do hire them, they'll give them a smaller wage than a younger person for the same job.