Itinerary Critques

Your plan is ambitious for 10 full days + 2 travel days. While it’s tempting to try to “see it all” when you haven’t been to Europe, if you try to do too much you’re going to leave completely exhausted and every time you move you lose close to a 1/2 day. There are ways you can accomplish things like seeing historic buildings while also consolidating some of your itinerary. You don’t need to do Zurich to see historic sites - you’re going to get that in Luzern and really, everywhere you look and Zurich is really not the best example of a historic city in Europe - it’s an international banking city not worth your time with such a short/tight itinerary. Places like Luzern and Thun are way better for what you're describing. Also, some of your days are unrealistic because you’re not accounting for lines, transportation, etc. For example, the Northface Trail can be done in around 2-2.5 hours if you speed through the whole thing, but then really what’s the point? You’re going to want to stop a million times to take photos, trust me :) And it's not a completely flat walk, so you're going to want to take breaks + visit the little farms where you can eat/drink along the way.

I don’t know anything about Heidiland, so I’ll leave that part to someone else to comment on, but I will suggest on the rest….

At the very least, you should skip your night in Zurich and add it to Murren to accomplish your list. — 4 nights Murren > Luzern 2 nights > Varenna 3 nights > HeidiLand 2 nights

Day 1 — Land in Zurich and head straight to Murren - store your luggage and if it’s a nice day, go up to Schilthorn for epic views or an easy walk down to Gimmelwald to stroll around exploring -- these activities will be the epic beginning to your trip you're dreaming of
Day 2 — You’ll be getting over jet lag, so I recommend sticking close to Murren after a long travel day and doing the Northface Trail + either Schilthorn or Gimmelwald if you didn’t get a chance to do any of those on your entrance day — To make the NF hike easier, ride the Allmendhubel funicular up and then do the hike counter clockwise, it’s easier that way.
Day 3 — Murren > Grutschalp > Lauterbrunnen > Wengen > Mannlichen > walk to Kleine Scheidegg > optional Jungfraujoch (personally I recommend skipping, Schilthorn is better and less of a fiasco to do) > train back to Wengen > Lauterbrunnen > walk to Stechelberg (see waterfalls along the walk, Trummelbach Falls is only worth the line if it’s a rainy day) > cable car from Stechelberg to Murren
Day 4 — Grindelwald First (if you’re okay with all of the lines & crowds) — I like Schynige Platte better personally and the hike has views of the lakes and mountains along the ridge — or if you want more historic town time, do a day trip on Lake Thun to see castles at Oberhofen, Spiez and Thun + the historic Aare riverfront
Day 5 — Murren > Luzern — explore all the historic sites (walk the Musegg historic wall for panoramic views over the old town)
Day 6 — Vitznau/Mt Rigi
Day 7 — Luzern > Varenna
Day 8 — Lake Como
Day 9 — Lake Como
Day 10 — Bernini Express/HeidiLand
Day 11 — Heidi Land
Day 12 — HeidiLand > Zurich Airport

I agree you need to slow down and actually be present in a location. Your pace will get really old after the first week. You need flexibility for weather, the usual head cold, laundry, jet lag. You may not be sleeping well the first few days.

I would skip Zurich and Heideland. I have read Trip Reports and recommendations on this Forum for years, and have never seen that recommended.

I'm having a little trouble following your itinerary, as it is recommended that one counts nights, not days. Sorry I'm confused. You have done a lot of research.

Your incoming flight could be delayed and that whole day lost, that's happened to us.

So -
Lucerne, Murren, Lake Como,
and maybe one night in Zurich if you have an early flight.

Keep it simple. You'll enjoy the trip more and remember more. You'll be there at a fantastic time, so enjoy, make a decision, and book accommodations asap.
Safe travels!

An alternative option if you’re open to skipping Heidiland (the name is fun, but other than saying you’ve been there, I think there are better options), is to focus on Murren and the surrounding historic sites & mountains + Lake Como with your niece and then do Luzern on your way back to Zurich.

Day 1 — Zurich > Murren (Gimmelwald or Schilthorn)
Day 2 — Northface Trail + either Schilthorn or Gimmelwald if you didn’t get a chance to do any of those on your entrance day
Day 3 — Mannlichen/Jungfraujoch
Day 4 — Day trip on Lake Thun to see castles at Spiez, Oberhofen & Thun + historic Aare river front
Day 5 — Grindelwald First or Schynige Platte
Day 6 — weather buffer for all the above activities or optional day trip to Lake Brienz to see Giessbach Falls + historic hotel, historic street in Brienz, Ballenberg Open Air Museum
Day 7 — Murren > Varenna (option to store luggage in Luzern on the way if your niece wants to see it for a couple hours -- you can hit all the major sites in the downtown in around 2 hours)
Day 8 — Lake Como
Day 9 — Lake Como
Day 10 — Lake Como > Luzern (option to stop along the way, store luggage in Bellinzona to see the castles or just extra time exploring Luzern)
Day 11 — Luzern — historic area and/or Vitznau/Mt Rigi
Day 12 — Luzern > Zurich Airport