Border collies are more work than you can imagine. Imagine how much a very active dog would be, and then times it by 50. Over and over, I meet people who took in a border collie or herding dog or a 50/50 mix and it turned into a nightmare, but both animal and owner. A friend in the city got herself an Australian herding dog, called her a cute name and she was very pretty. Within two years, she had to have the dog euthanised because he went stupid from not enough exercise or attention. A girlfriend back in NZ had a border collie and it became so destructive, she couldn’t keep it. A neighbour here in my village in Norway got a female border collie/retriever cross and it is two years old. He is a retired guy, and has spent time with the dog, but it is completely out of control and he has never had the heart to treat the bitch in a way she could be trained because he thinks those methods are ‘cruel’ yet, he has brought her to the vet twice with the intention of euthanising her because of how out of control she is. (This dog I think of when I wake up every morning and wonder if I should take a hand to her and try to train her, simply to save her life. She is beautiful, but completely wild.)
Maggie might be a calming influence and herding dogs need company 24/7, so that could be a real positive but what if they don’t get along? Dogs are very much like poorly communicative people. If they decide they don’t like a new comer, it is difficult to fix.
If you have a local dog trainer you can talk with and who might be able to guide and fix problems as they occur, make use of them. Dogs are pack animals and they all have different personalities. Breed traits are strong, because it’s in their genes to be that way, so behaviour correction can only do so much and it will be harder than you think.