Starting low carb...

If you're going zero carb (which is extremely difficult) then remember that you will have to consume a lot of healthy fats in order to get energy.

Basal will need reduced providing that you're daughter also goes down the "very low carb route". I'm not a pump user so I'm afraid I cannot advise here. I would imagine however that there would be a greatly reduced need for pump therapy if she cut the carbs out totally. She could do the once/twice daily basal injection like the rest of us on MDI.

It's possible to low carb but still enjoy some carbohydrates. If it were me, I'd stick to a limit of around 40-60g carbs per day. That way you'll still be low carbing, not run the risk of feeling drained and tired and most importantly - not seriously restrict your food choice options.

Grant

I don't see why you would return to pens when low carbing.

What do you mean by very/fully low carb in terms of grams of carbs per day?

Reducing carbs dramatically is likely to see a reduction in basal rates. But by making that reduction with the pump, you would get to keep the bespoke adjustments of your pump basal rate to match needs as they vary through 24 hours, rather that the flat line basal which the MDI background insulins aim for.

Also, if you are taking in very few carbs per meal you might find you need less than a unit or even half a unit as your bolus - you can take 0.05 on your Omnipod, the lowest with MDI is 0.50 - big difference. Also the pump will let you play around with extended boluses which you might find more necessary when low carbing if you start to find there is a need to bolus for protein which might create a delayed peak in someone who isn't eating a lot of carbs.

You might also want to have a look a low carbing and puberty - I don't know anything about it but it's just something to consider - whether cutting out a nutrtition group in childhood/puberty could have any implications (positive or negative - I've not got an agenda to push, I genuinely don't know) for development, fertility etc.