Are you so drunk with tetosterone that violent force is your only option? Get real, pal!
Joan is a female Kindred. No indication show that she got combat skills. Hell, she's barely better than normal Kine, at that. The gun? What a laugh. She has no training, more than likely she will fumble that first-time-ever-touch-it gun. Direct action is out. O.U.T. You want going in gun blazing you should have chosen others, not a Sabbat spy in a Tremere chantry.
Second, she's a spy, not direct action specialist. Her main occupation will be gathering info, not running around doing dirty deeds for strangers which drawing undue attentions from Kindred and Kines alike. She need to do this event, true, but that doesnt mean she has to draw notices from a messy killing. Out of all options convincing the gal to leave London is the best there is in term of pumping her for informations.
A is tricky since Joan doesnt seem to know
D and C is very tricky in term of humanity-loss. Massacre usually sucks.
B is even trickier: Joan is just not dominating or charismatic to lure a mother out to the park at night, leaving her children at home.
Only E allow Joan getting some info of what's going on.