Many dogs love their crates.It resembles a den they would seek out/build if they didn't have cozy houses to live in. It's probably the only place in the house that is truly theirs, where they can be undisturbed and feel safe. You don't mention how old your dog is, but like people, as dogs age they tend to get a bit less social and less playful. Before, having all of you in one room may have signaled play time, and now she may be thinking, "sheesh, play time? I think I'll just go to bed." It's also possible she's avoiding one family member in particular who behaves in a way that makes her feel nervous, overwhelmed, or uncomfortable. Neither of my dogs bonded much with my ex when he lived with me, even though he was never mean to them. They both have a preference for women, and so they were just never as comfortable with him. We'd see the opposite pattern you're describing - they would be out and social when both of us were here, but when I was out of the house and only he was here, the dogs would spend almost all their time in their crate, only coming out when he would feed them or take them out.
Although dogs can suffer from depression, if this is the only sign you're seeing, she's probably just doing what makes her most comfortable and her preferences have changed as she gets older. If it's important to you that she spend time with the family when you're all together, you could try putting a big comfy bed in the corner of the room for her and giving her a special treat, like a stuffed Kong or a chew toy while she's there with you.