According to Ender Canon, Mazer Rakham won a Second Formics Invasion by figuring out the pattern and finding and destroying the Bugger Queen's ship.
But as we find out later:
Formics' Queens can communicate with the "worker" buggers via philotic connections
This communication is instantaneous across any distance.
So, given this:
why was the invasion-commanding bugger Queen situated right there in Solar System where she could be destroyed in the first place?
I'd prefer an in-universe answer or at least an authoritative (e.g. from OSC) one, not a speculation.
UPDATE: Please note that "The Formics didn't realize that the queen was in any danger and thus needed to be protected" seems to be 100% wrong according to "Ender's Game":
Ender : "They make that ship move just like any other ship";
Mazer : "They know it's their weak point."