I've wondered the same thing.
Is your friend planting 'burpless' cucumbers? Those are the only ones that do not have a bitter note for me. They have low cucurbitacin content, which is the chemical responsible for the bitter taste in cucumbers.
It is naturally found in the entire family of squashes, pumpkins, melons, and gourds. The higher the temperature outside, the more it forms in cucumbers, hence the bitter flavor. The older and bigger they get, the more they have.
It's definitely cooler where she lives than where I am and she's tried several varieties.
Last year she planted Munchers from seeds that I sent to her so they should have tasted the same as the ones I am growing.
I make sure to pick them before they have any yellow but I don't have any issues with my cucumbers getting bitter otherwise and I planted like 12 varieties this year, lol.
You can rub the cucurbitacin out of the cucumbers. I do that when I wait too long to harvest.
Armenian cucumbers never seem to get bitter even when you allow them to get enormous because they're more like a melon.