Adult Giant Schnauzer - potty training issue... or incontinence?

I am looking into adopting a 4 1/2 year old (spayed) female Giant, as a companion for my 8 year old male lab. I am well aware of all the good and bad that comes with the breed, but I am single with no kids, very active person, good at training dogs so I don't think we'll have any issues there...
The people who are giving her up (due to inability to spend time with her and to give her attention that she needs) claim she is the sweetest, gentlest, giant lap dog ever, with a small problem (of course, there is always something, right?!): she occasionally has accidents in the house (always on the kitchen tile... and always at night). Is this something common for this breed? There are very few online sources addressing urinary incontinence... I'm curious if this may be a spite/anxiety issue or if it's more of a medical one. I'd love to hear from GS owners, has anyone had a similar experience? Can an adult dog really be re-trained successfully if they've been allowed to get away with accidents all their life? Should I be up for this challenge, or move on and wait for another GS to come along? Thanks.

You might want to talk with your vet. If it is incontinence, there is medication (Proin) that can be used to help. Our Mini Schnauzer was on it for a couple of years, and it definitely made a difference.

There's little you can do to prevent incontinence--you can only deal with it once it arises. In the case of submissive urination, the best advice is to keep a stress-prone dog out of situations that may lead to an accident. Never punish the dog for his behavior, as that will likely make the problem worse.

http://dogtime.com/incontinence.html