Back to the Future: The Game - 30th Anniversary Edition

Episode 4 - Double Vision

At the expo first Speak to Edna and Arty and you will see Trixie come through the doors.
Now speak to Trixie and exhaust the dialogue options.

Go back to Edna and Select 'I just spoke to Trixie' Edna will be furious. Now Select 'You want to get Trixie Fired?'. This will unlock Cueball who appears by the truck.

Go over to Cueball and select the Trixie related dialogue options and he will give you a postcard of Trixie. In your Inventory go to the postcard and press X to examine the postcard to unlock

Which is Missable.

(On a sidenote Make sure you get the Algae cakes off Cueball for another missable achievement Let them Eat Cake)

Now, Take the postcard over to Edna who uses it to get Trixie fired. Trixie now agrees to split up Edna and Emmett, she just requires three props:

In the Lab with Emmett. Select the Easel. When he asks you if you like the photo Select No you dont. Emmett will place his photo album on the table, go and pick it up. After returning from the lab with the Cleaning Spray go to the Hill Valley of the Past Exhibit. Use the Spray on the Caveman. Now select the caveman again and you will pick up the furs. Finally go over to the Hill Valley Future Exhibit, press buttons 3 and 4 I believe. This will unlodge the diamond.

Give these three items to Trixie.

After returning back from the lab a second time. You are required to throw oil over Emmett's suit. This will start a cutscene where poor Emmett loses Edna thanks to Trixie and her props. But you get your Achievement.

I really hope this guide was helpful, I dont normally write them however their was a lack of clear info and their are quite a few steps. If you