I think all I could say is "I am so sorry". If you need to give her comfort regarding his suicide, you can tell her that God knew his heart and must have known, truly known, how badly he was hurting.
I am so, so sorry, Cheryl. If you can, send flowers and a condolence card right away. I lost my brother in law last year (DUI, unfortunately) and I have followed my sister's lead. I do not discuss the DUI with her because she's never brought it up to me. What I focus on, when she wants to talk, is her feelings and the fact that, no matter how it happened, the death is a real, very painful loss. I call and sometimes she answers, sometimes she doesn't. Sometimes she's in the mood to talk, sometimes not. Let your 'sister' lead you, and just keep keeping in touch.
What my sister would tell you:(pointedly honest)
Do not tell her it's going to be fine or that it's going to make her stronger or that she'll find some purpose in this death. My sister basically wanted to slap those people.
Do not tell her she needs to 'take care of herself' or 'needs to eat'. She doesn't want to eat. Sleeping is hard for some survivors of death, and her sleeping may bring on nightmares. She's going to be in shock for a while.
Do not ask 'what can I do?' open-ended questions, if you can help this. My sister told someone "you can bring my husband back to life for me". Not a comfortable moment. If you want to offer her things, ask about specifics. Food, gift card to a Kroeger market, money for a babysitter for the kids or a dogwalking service. Or just send a check if you can. Funerals and memorials cost a lot of money.
Do not tell her to get on with life, to 'get out a bit'. Getting out means breaking down in tears in the car, falling apart in public at the grocery store, and anything can be a trigger for emotionally losing it.
Just keep calling. Just tell her you love her and are thinking about her. Keep telling her to call if she needs anything. Just let her know you are available and love her.
Once again, I am so sorry. Sending you hugs and strength.