Hi. You might want to post a photo of Soup...it might help to get opinions on your baby. Besides, we'd like to see her!
The standard for a Yorkshire Terrier is that of a blue and tan dog that cannot have more than 1" of white in any direction and only on the chest. More white than that is a disqualification. Parti-colored Yorkies cannot be shown in conformation AKC shows. You can search on the internet for the Yorkshire Terrier Club of America (YTCA) and/or the American Kennel Club (AKC) for the full standard. However, there are some absolutely gorgeous Parti's out there...and here on YT, also !!!
The answer that some dogs like water and some don't is right on...find out which is your Soup's attitude. If she likes it, make sure she is protected. If she doesn't, make sure she is prevented and/or protected from anything accidental causing a serious issue. You might want to train her for the water anyway, and as was suggested, make sure she can get out if she falls in accidentally. Swimming is, I believe, a natural instinct for dogs, but so is fear and some have more of one than the other.
Besides, there are really cute doggie swim items you can check into, too.
I am wondering why your "friend who raised poodles...always said that Parti-Poos were not a good thing" though. Did she elaborate at all as to the reason? I am just curious, mind you...!