This actually happened to me... I was about to beat it on Lunatic when I was attacked by 2 giant Flandres, they where strong, they absorbed the damaged they did and they had AoE attacks so they full-healed after killing all my dolls easily... I died 2 waves later.
Flandre is actually pretty overpowered in that game I can beat lunatic only using her alone When upgraded highly, she can even beat any giant one and their troops alone without even reducing her HP