My first question is, are you absolutely positive it was her pre-lay shed? I have been fooled by building myself, it's certainly an easy thing to mistake sometimes.
I mistook this building for an ovy:
Then about a month later I saw this...
Another building picture
Your best bet is to look for the tail suck when you think you see an ovulation
Another tail suck
You could actually see her eggs/follicles during her ovy (she laid 4 eggs)
And finally, right before they lay, you can tell there are eggs near the end. This girl was 1,600 grams and only laid 3 eggs. They move the eggs down their body before they lay.
If you pick them up, you can see their prego bellies
They get the ridge back/tent look
And another female close to laying, notice the ridge back/tent look