Exit/Reboard a train en route ok?

You can exit and reboard with the same ticket as long as the ticket you purchased is for the route you take. She should buy a ticket Zurich->Wengen via Basel. But instead of her backtracking to meet you why don’t you just plan to meet up at a common point along the way such as Olten?

What kind of pass are you buying?
Or are you buying point to point tickets?
There is no direct train Basel to Wengen and it is on a different rail line than Zurich to Basel.
It might be more convenient to meet her in Interlaken or Lauterbrunnen.
Lauterbrunnen is where the train to Wengen originates.

No.

Or at least, yes, but she would need a ticket from Zürich to Basel and another ticket from Basel to Wengen, because the route from Zürich, or even Zürich airport, does not go through Basel. That would be way out of the way so she will have to pay for that.

The normal route from Zürich to Wengen would either be via Bern (your train will go through there, so yes she could get off there and board your train in Bern, or you could both get off and have lunch in Bern and get on another train after lunch - for no extra cost unless either of you is travelling on a special discounted ticket in which case, no) or Luzern. You couldn't meet her in Luzern for no extra money because the normal routing from Basel to Wengen is through Bern.

Does that make sense?

or, to put it another way - the answer to the question in the title of your post is generally YES; the answer to the specific question in the text of your post is NO. The problem is that it is not en-route.

I agree with Nigel. The route from Zürich to Wengen does not go via Basel, it is in a different direction. You have to pay for the extra distance. It is simple enough to buy 2 tickets.

Interlaken Ost station would be a better meeting point, in my opinion.
- Less backtracking and cheaper for the daughter.
- Bern was floated, but Interlaken is a smaller station than Bern, and removes the need to get off at Bern (many trains are direct from Basel to Interlaken)
- Ability for daughter to take scenic route via Luzern and the 'Luzern Interlaken Express', it's not more difficult than the normal route, but a bit longer.

Why not just meet up when you get to Wengen?
Better than sending your daughter in the wrong direction (to Basel), then doubling back again. Plus the issue of ensuring you both meet up at the same place and time somewhere in Basel.

Thanks for the quick replies! I obviously need to become more skilled in using the SBB timetables.
Our only plan at this point is to buy half-fare cards. My daughter is scheduled to arrive at the Zurich airport at 11:30 am, but our arrival time (by cruise) is uncertain. I assume it would be simplest for my daughter to get the train at the airport. Would this affect her best route to Wengen? I think simplifying things for her should be our priority.

When you said your daughter was arriving at "Zurich", I suspected you actually meant Zurich airport. As far as train travel is concerned, these are two different places.

There is at least one train per hour on all rail routes in Switzerland, in many cases two (one every 30 minutes). There is no need to worry about when the train is, just turn up at the station and get the next one.

If you go to the SBB (Swiss Federal Railways) website: https://www.sbb.ch/en
This will always give you the quickest route.
Enter from: Zürich Flughafen (this is the name of the station at the airport, "Flughafen" is German for airport)
To: Wengen, and your daughter's arrival date, and a time of ~12:30 (to allow time to disembark, get through immigration etc.), then it will list all the trains.
If you click on one of the options, it will expand it and show the individual trains, and where and when to change.

You can do the same thing to get he times for Basel to Wengen.

Here is a rail map of Switzerland: https://www.sbb.ch/content/dam/sbb/de/infotexte/uebersichtskarte-sts.pdf
You can trace your routes on it:
1) Zürich Flughafen - Bern - Interlaken - Wengen
2) Basel - Olten - Bern - Interlaken - Wengen.

Thanks to all.