Glad everything is going well with pups and mum!

I had a litter in March and mum didn't want to leave them for the first week. Then on day 7 she went to the front door and made it clear she was ready to go out for walks. So I would always go by mum. I would say that if your girl is being destructive then it's definitely a sign that she's in need of some space and ready to get away from them for a bit and as you said she's used to getting a lot of exercise (much like mine) so she will be more inclined to get out for a walk. So I would say yes to taking her out for a 10-15 minute walk, make sure all the pups have fed and are content, if you're worried and have a spare person then get them to stay with the pups whilst you're out, and then go out with her on/off lead whatever she's used to and what you think is best (for me that was off lead and she was perfectly normal). At this stage I'd even think about taking her out for a 10-15 minute walk in the morning and then again in the evening. Then when you're back get her in with the pups and you'll notice a difference straight away! It's amazing how a little time away can encourage them to want to be with them more! Mine loved her walks and was eager to go out but then once we got home afterwards so couldn't wait to get back in with them...that was until they developed teeth!
But do remember to have a disinfectant solution ready for when you return from the walk as she'll need her milk bar, legs and paws wiped down with it before she goes back in with the pups.
Remember that mum (if she's a good mum, which it sounds like she is) knows better than we do, even if we think we know better. Listen to mum, remember that she doesn't need to spend 24/7 with the pups. If the room is the right temperature and they've been fed and content then if she wants to get up and have a wander round and have a lie down in a different room then that's fine. Anyway gradually increase her exercise as the pups get older. It sounds as though you're doing great so well done, hope they continue to thrive and that mum enjoys her walks!