Volcanic Queen

This might seem like a stupid question, but with Volcanic Queen's effect (This card cannot be Normal Summoned or Set. This card can only be Special Summoned from your hand to your opponent's side of the field by Tributing 1 monster your opponent controls. If you Special Summon this card, you cannot Normal Summon or Set this turn. Once per turn, you can send 1 other card you control to the Graveyard to inflict 1000 damage to your opponent. During your End Phase, either Tribute 1 other monster or take 1000 damage.), can my opponent activate the 2nd effect even though she is now under my control? I got ASSed because i said he couldn't.

since when can your opponent activate monster effects from monsters under your control? Of course he can't...

that's was i thought
i just wasn't sure, since ive never dealt with Volcanics before.

The first part of the text: "This card cannot be Normal Summoned or Set. This card can only be Special Summoned from your hand to your opponent's side of the field by Tributing 1 monster your opponent controls. If you Special Summon this card, you cannot Normal Summon or Set this turn." is the summoning condition for Volcanic Queen, so it belongs to the owner of the card. The remaining part of the text is the effect of a face-up Volcanic Queen, so it belongs to whoever controls it.