When Marge first came here, it was Layla's decision, ultimately, if Marge was to stay. If bringing a dog into a house with a cat who had been here for a decade alone was too much, I would have respected that. She also has allergies, so that was a very large consideration as well.
I'm not really sure why she decided to let Marge stay. The whole first day Marge was here, she was astonishingly comfortable with her presence. She did tend to stay high up on furniture, but that wasn't bizarre behavior for her, anyway.
As months go by, the relationship between cat and dog has grown. Marge always wants to play with Layla, but usually gets greeted by pinned ears, angry eyes and a swatting paw. Honestly, it doesn't scare Marge away very well.. I've caught her going down into play bows around Layla on multiple occasions.
The thing I'm most happy about is that Marge and Layla can both cuddle up with me on the couch. In the beginning, Layla wouldn't come sit on me if Marge was laying next to me. Now, I can fall asleep on the couch at 12 AM (like I so often do) and wake up to fur all over the place. I wouldn't want it any other way!