I know lots of people the same age as your DM. My first thought was that 4 hours at an attraction would be long enough for many of them. Also, having people to stay, especially including a child and a baby, when you're used to living alone, is not something that's easy to take in your stride.
At her age, when she's obviously still coping with bereavement and the adjustment to daily life on her own, even the most laid-back of people start to over-think and worry about things going wrong so they can reassure themselves that the worst-case scenario is covered.
I don't see her behaviour towards you as controlling. It sounds as if it's only when you impinge on her life. My DM would insist I rang her when I got home from visiting her - as if that was the only time I might crash the car. She obviously knew I drove on a daily basis, but somehow she wasn't involved in that.
She does need to see her GP. There's evidence that the body struggles with serotonin levels as people get older. A low-dose of an anti-anxiety pill could make things so much easier for her.
I think you should park the egg-donor issue for now and also your feelings about your childhood. They just complicate a difficult situation and bringing them into the open won't improve it, for either of you.
Focus on reducing her anxiety. Prioritise the GP check-up. If necessary, I'd go so far as using the threat of a hotel stay next time as leverage to persuade her to make an appointment, on the grounds that you feel it's too much for her while she's so anxious and she needs to get help.
Otherwise, I'm afraid you will have to fit in with her when you visit. Just suck it up. Her need is greater than yours at the moment.