A few things from a fellow big dog/small dog owner.
1. How long has this been going on or has it only been the 2 times? My Piper had a horrible 2 week span. I didn't know what the h*ll was going on with her. She would also just pee- where ever, when ever. Finally one day it just stopped again.
2. I would suggest (even though may be more work) outside training. She sees your Dane go out. Try bell training. This way you know when she needs to go.
3. It is really different potty training a big dog vs. a small dog. Duke can hold it for hours and hours, Piper if running around can't hold it very long and when she needs to go, she needs to go. If we don't let her out within a minute or so when she rings the bells, she will pee by the door.
4. Try an x-pen. That way she can see your Dane and even interact with him a little, but is still confined.
I really do feel your pain, as it is so very different with a large dog vs a small dog. (My mom calls Piper, pee pee Piper, or pee pee for short, because of the first few times I took her to my parents)
If nothing else, start ALL over. Confine in a crate at all times if you can't watch her. Tie the leash to you.
If nothing else, stick a diaper on her
I've done that as well when we first went to my parents.