Schiphol and Frankfurt are both huge airports. Even at the best of times they feel crowded and busy. Non-Schengen to non-schengen, should be easy though.
I personally would avoid a combi, if I had a choice. KL into KUL on a combo we had to wait until they off-loaded a couple of pallets from the main deck.
Zürich, on the other hand, isn't huge. A 45 minute connection, even between the furthest gates, is easy - and the bags make it too.
On the way back she can shop 'duty free'. (Swiss prices tend to be higher than the ROE (rest of Europe), but without duty and VAT should be a lot lower than UK high street prices. I don't know how these prices compare to BJS though.