This isn't a competition, I'm trying to understand why you want to run her.
Fueled by corpse counters which she needs to somehow pick up. As you've pointed out, she's very slow. The likelihood of her ever picking up 2 corpse counters that weren't from your own models is slim, and even if she does, she's going to need to waste at least one valuable (1) action on picking them up.
Needs an 8 crow to cast, a very valuable card in Rezzers.
Her signature ability really. However, it needs a 7 mask to cast. You cannot rely on flipping a mask to do this regularly, so you have to normally cheat one from your hand; and McMourning also wants masks for Scalpel Magic. If this ability was suitless, she'd be amazing, but as it is she struggles to cast it more than a couple of times per game at most. It's incredibly unreliable. You'll see this when you play her more.
No doubt. But again, sacrificing your 9 point model plus needing to cheat a very high crow (highly in demand in Rezzers and particularly McMourning), can you rely on this working when you need it most?
Why useful against them in particular? Pitiful is good, perma-pitiful thanks to Uncontrolled Crying is better, but you can't really rely on it, especially with her low Wp of 5.
Basically, Molly is very hit or miss. She's not fast, she's not tough and she's not good in combat; she's a support model. Unfortunately she's a support model that has a suit requirement on every spell, and moreover, has suit requirements that directly detract from the suit requirements of the other models in your crew. Using a Molly spell doesn't just mean needing to cheat, it also means reduced effectiveness for others who would have used that card. She's very, very hit or miss, and from experience playing her, I havent played a single game where I've took her and not thought "I wish I had something else".
Molly is absolute Fool's Gold in my opinion. She looks great on paper, but in reality she's not.
That looks familiar Though Dead Rider is very definitely not core.