From Ljubliana to Kotor 14 - 21 days

There are hotels directly in the park at Plitvice. Get off the bus and walk to the hotel from the road - not far. Then walk right into the park. If you had a car to park, you'd do the same walk into the park from the parking lot and right past the hotels (at Entrance #2 anyway).

Plitvice park hotels seem to be booking early, so I would book one ASAP. (Try a site like Booking.com which lets you make refundable reservations on many hotels, if you cancel a few days prior to check-in. Read the terms carefully, they vary per property.)

The park will be very popular in May so busy mid-day. It's really best to get into the park at 7am when it opens (easy to do if staying at one of the park hotels). Best strategy is probably to see the park over two days: the first afternoon see lower or upper lakes; next morning, see the other part. I think the last bus to Split leaves pretty early in the afternoon as I recall (one with a connection in Zadar may leave later). But you can get out by noon the second day if you've seen half of it the first day.

There are no trains to Dubrovnik. You'll either take a bus or ferry/catamaran south from Split.

If you are sticking around after your daughter leaves, you could always head up to Bosnia - Mostar and Sarajevo, etc. With a whole week, you could bus over to one of the little towns like Jajce and maybe back to Zagreb and fly home from there. Mostar is pretty touristy, but otherwise it's a very different experience from touristy Croatia.

I did not know that there are hotels an easy walk to the parks. I did Plitvice as a day tour and felt I had plenty of time to see the park.
I highly recommend staying right outside of DUB and taking the bus in under 15 minutes to the gates. I took a great day tour to visit small towns not easy to access with out a car.sending details in a private message later today!

I would recommend staying within or right outside the walls of the old town in Dubrovnik. The town is very crowded and touristy during the day with cruise ship tourists, but at night it quiets down and really glistens with the lights reflecting off the polished stones of the streets. If you take a bus in, you'll miss that easy walk at night unless you stay really late, and you'll probably hate Dubrovnik if you see it only with the Disneyland-like crowds. I've done the "take the bus into Dubrovnik" approach too (second visit), and while it is doable (and buses run fairly late), I only did it because I had a car on that trip, and parking right at or near the old town can be a huge hassle and expense. Without a car, I'd most definitely recommend staying in/at the old town. I stayed right outside the Pile Gate the first time - very flat, no steps to deal with, close to the local bus stop.

Thank you all. I have reversed the order of the itinerary, and now I'm thinking it would be better to start off in the south, in Dubrovnik, because it might be a little less crowded than later in the month. By the same token Ljubljana might be warmer towards the end of our trip. So now I'm thinking of taking a bus from Dubrovnik to Zadar, staying there a couple of nights, instead of Split, and taking a bus to Plitvice, since the trip is much shorter from there. How does Zadar compare to Split in beauty, etc.? We might stay 2 nights in the park , since we think the scenery would be very relaxing and enjoyable. (I've already booked a hotel inside the park since availability was rapidly shrinking ). There's free cancellation up to 3 days before we get there, just in case. From Plitvice we would take a bus to Zagreb, stay one night, and leave early the next morning for Ljubljana. Your thoughts?

I would definitely prefer Split to Zadar, personally. I did not really love either city, but Split has many fans, and it is clearly more significant and offers more day trip options (to islands, etc.). Zadar has some Roman ruins and a few other interesting features, but I really don't think it compares well to Split. I can't imagine wanting to spend three nights in Zadar.