Baldur's Gate 3

The other guide, which details ditching the eggs before ever engaging in combat, is a good one, but here's another way: If you have an invisibility spell available to you, turn invisible and sneak right on over to where the Matriarch is walking around. Then, use a spell with some knockback (or possibly shove, though I'm not *entirely* sure that'll work) to push her into the endless-ish chasm below. I used thunderwave, and done, just a couple surprised little phase spiders to ditch after that. The eggs just sit there, undisturbed.

(Also, fear not, loot addicts, the body of the matriarch isn't lost forever.)

Just a heads up, all the current Steam and early access guides list this as unlocking after destroying the egg clusters and then beginning combat with the matriarch, but this has been patched - you do indeed need to actually kill the matriarch now for this to unlock properly.

There are three clusters of eggs - one on the pillar where the matriarch stands, one on the pillar beside her connected with a spidersilk bridge, and one down a floor below underneath the third pillar. Use the Spiderstep Boots or similar to cross the silk bridges without alerting the enemies and snipe all the eggs before beginning combat.

Kill the matriarch after destroying all the eggs and the trophy is yours.