So here's a thing, my sister just had two kids at 48 naturally, how the hell is she going to cope with small children and the menopause as she is now starting it - I can tell as I've been there and turned into something out of the exorcist - although luckily I had my baby age 20 so he'd left home long before then.
People are all different. We don't know your sister so we can't tell you.
Some have more energy in their late 40s than others in their mid-20s. Some hardly notice the menopause: I had no mood swings, no physical symptoms, no sudden sense of ageing or changing, and I am pretty sure that none of my colleagues or family could have told I was going through it.
Others actually feel more energetic after they've gone through it than they've ever done before: my dm did.
Some find small children exhausting, others not so much.
I wouldn't worry too much about it; just be prepared to lend a helping and non-judgmental hand as you would with any new mother in the family regardless of age.