New Here - pollymorph question

[RexCalibvr]

So trying to work out the finer rules, the faq was very helpful... but so much unanswered.
Playing with my two teenagers, I decided to help my daughter with a battle, my boy then added a 2 level monster, we managed to get the strength to beat them both.... but then i realised she would win with the added levels (we let her have the win as we were unsure of the next bit).
So i suggested playing my pollymorph to remove the 2 level beast, but because i was the one helping her and we were already strong enough, from what i read i couldn't play it as we were winning the fight, but on the other hand it would be very munchkin like to take it from her even tho i was helping.
Clarification?

Thanks

[Andrew Hackard]

Being a helper in combat doesn't remove your agency. If you realize after you join the fight that you're going to help someone win, you're allowed to make the monsters tougher or otherwise take an action to try to remove the winning condition from the combat. You don't have to be a totally helpful helper, if that makes sense.

[RexCalibvr]

Thank you Andrew, appreciated