If the State of Colorado have no notable women in their political circle to be a Senator then that's fine - maybe in a few years they will.
Freedom of choice means not everyone has to be one or must see it as being qualified.
Being in congress is a choice - a path - and not a requirement of anyone but a desire that must be fought for.
To your other questoin in the OP: what type of difference will it make - it won't make much of one to have 'more balanced' numbers of women vs men - we're talking about an increase of few people if the #'s of members stay where they are. If we increased it to 100 we're just constipate the system - nothing would ever be done, can you imagine? I can: ugh!
They represent their states, women these days don't necessarily have a collective view or value we fight to uphold or something like women's sufferage or the right to be paid the same wages - because of changes in our society towards women it's not necessarily like it once was - in fact, it's never been that way. Senators represent their states and their political parties, etc - just like the men do. I don't think it would make as much as a difference as you're imagining if we had a few more and they had a few less.
That's really just suggesting that men can't vote in favor of certain bills and such that effect women - of course they can. They can and they do. That's also like saying women can't vote for something that might be seen as challenging some of these 'gained rights' (like abortion) but we gained the right to vote, started reshaping views of women and mothers in general and so on with only one female representation in Congress near that time: Jeanette Rankin. . . and she was out in 1919 - and some women believed she'd HURT the women's sufferage efforts by being there!
Other countries might have different rules - that's fine - we're the USA and they're whoever they are. It's ok for us to be different.
What's next - wanting gender-representation in the presidency and vice presidency: instead of 1 there should be 2?