My daughter is studying at University of Edinburgh this fall and we are planning a trip to see her in mid to late October. She doesn’t have a break so we will need to entertain ourselves during the day and I am looking for some ideas. We will likely want to rent a car to see some of the Highlands. The point of the trip is obviously to see my daughter, but I don’t mind taking a day trip and spending the night elsewhere. Thank you!
Is there a question? You might take a look at Rabbie's, a popular tour operator. They single- and multi-day trips. https://www.rabbies.com/en-gb/tours/scotland/from-edinburgh?startTimestamp=1792022400&endTimestamp=1793491199
Although there are day tours that will show you a bit of the Highlands, you really need at least an overnight to enjoy yourself.
Without a rental car, you could take the West Highland Railway Line from Glasgow to Ft. William, Mallaig or Oban. You'll travel through some lovely highland scenery. The journey from Edinburgh is about 4 hours.
Where you overnight would depend on your interests and your time.
With a 2 night stay in Oban, on the coast you could do a day trip to Mull and Iona.
With Fort William or Mallaig you could see the Glenfinnan Monument and the famous Viaduct (you travel over the viaduct enroute to Mallaig) or maybe a gondola ride to the top of Ben Nevis.
With a rental car, you will have more options depending on the time you have available.
How long are you planning for this visit?
Have a look at this website that has suggestions for driving tours . Many can be done from Edinburgh.
Pitlochry and Rannoch would need to be done from Pitlochry.
Use Oban as a base for the Oban and Inverary tour as well as the Oban and Glencoe.