Researching Western Australia

We dock in Perth on March 15 and expect to be off the ship by 9 am. I've rented a car and will pick up in Freemantle.Dr Clark departs Perth that day to fly home so we'll be meeting him & Lise for lunch before he heads to the airport. Decisions, decisions...should we spend the afternoon in Perth? We have an overnight reservation at a Mandurah beach resort which is about an hour south of Perth and I want to see this area. The following day we will head south to see Jill (Clark) Grist who, lives about 2 hours south from Mandurah. We'll make a home base at her place for 4 or 5 days. Really looking forward to seeing Jill. It's been over 30 years even though we've kept in contact over the years. She was my Maid of Honor. There's lots to see & do in South Western Australia and I really can't make a definite decision and it is driving me crazy