FYI, I think the Dasha/Dascha you saw is
Daria Zhukova, a model. The porn star's real name is
Dagmar. So Dasha/Dascha is kind of a pet form, maybe. Interesting.
On an American & English speaking woman or girl (I'm in the US so that's about all my opinion applies to), I'd like it okay. I like the sound of it. I have about the same impression as I have of a girl named
Sasha, or
Nikita, or even something like
Saskia or
Fleur -- it'd seem sort of self-consciously exotic, but in a 21st-century mainstream sort of way; not distractingly attention-grabbing, just pleasant.
I don't see a problem with the long Polish last name, unless it has a "sh" sound at the beginning. I suggest you try to find out in exactly what part of the world are women called Dascha/Dasha, though, just in case you or she should run into someone from there who is curious how a woman with that last name came to be called Dascha.
Combos ... well, barring odd initials, excessive length, rhyminess, and puns, I'm not really critical of combinations anymore. Try out the names of some other women you admire, or women in your family, with it. Some off the top of my head:
Dascha
Gloria Dascha Carolee
Dascha
MirandaDascha
QuinnDascha
MiaDascha
Darcy