My reasoning is twofold Callum, both from other judging experience.
The first one came up in a standard PPTQ where a player forgot his
The Scarab God 2nd Trigger (the graveyard one). As everybody probably know by now this is a required zone changed trigger, and even if missed it has to be resolved. the keyword here is resolved.
The IPG states : “Three types of triggered abilities do not expire and resolve immediately if they are discovered: (one of which is) A delayed triggered ability that changes the zone of one or more objects defined when the ability
was created. For this trigger, the opponent chooses whether to resolve the ability the next time a
player would get priority or when a player would get priority at the start of the next phase.”
Notice how the IPG uses the word “resolve” twice. This means that the trigger ability is resolved without using the stack, therefore you don't have time to respond to it. For the current scenario, the IPG states that “If the triggered ability isn’t covered by the previous two paragraphs, the opponent chooses whether the
triggered ability is added to the stack”
the fact it is added to the stack means the IPG specifically wanted players to be able to respond to it, much in the same way as activating a blinkmoth/inkmoth nexus in responce to a glimmervoid missed trigger is a perfectly fine solution.
That is why i'm saying that she can respond by blinking the Skyspawner, but she wont be able to choose the token since it was not on the battlefield at the time the trigger from the Eldrazi monument would have resolved.