Oh dear, Renee, that can be a tough decision, but one only you can make. First of all, it doesn't sound like this Hav was in the best of care. I mean, she's 5 and still has potty issues? Not to mention, she isn't even spayed?! Were they using her as puppy machine? You might want to ask if she ever had puppies, how often, and from what age.
In a way, you might be 'rescuing' this Havanese, but you should be prepared for issues that need your attention and commitment. I'm just guessing, I don't know ..... but I'd ask a few more questions before taking this female. The fact she is "free" is good, but only if a caring, conscientious person takes her. Some puppy mill or back yard breeder might want to snatch her so they can use her.
As to having two to train, if it's something you think you can manage, then go for it. Are you home a lot, do you have young kids that this 5 yr. old might not be comfortable around? Just thinking out loud......
Don't be shy to ask more questions and pls. let us know what comes of this, o.k.? I feel rather sad for the poor girl.