Plot card marched to the wall. If I discard shireen Baratheon can I kneel a character .

Margaery tyrell . When she kneels when blocking does she get 3 strength or she has to stay out of the challenge and kneel to give it someone else

Thanks

1) Shireen's text reads "when ... is killed". Marched to the Wall discards them (places them in the discard pile), not kill them (dead pile). Contrast with Viserys Targeryen, who says "when... leaves play".

2) Her ability is an "Action" with the cost of kneeling her. If you kneel her to defend, you can't use her ability. If it were to work the way you said, it would have to say "Reaction: After Margaery Tyrell is knelt"