Please Help! Rehoming a dog

My mum and sister sent me a message yesterday asking if I could look after one of their dogs puppies(she’s now 2). I know I wanted a dog but I didn’t want one yet, me and my partner both work 9-10 hours and day and don’t think this is fair on her. My mum and sister literally only have us a couple of minutes to make a decision and we felt bad saying no, as she was causing issues with the dogs in their house. Now we’re wondering whether it’s right for us to have a active collie who is nervous and likes a lot of exercise and attention, because we work long days. I’m looking for some advice and help on this. We want to keep her but we know there is going to be a better fit for her out there somewhere. This is not an easy decision but we want what is best for her

please help!