Oh man, the best you can do right now is probably talk to her and help her ventilate. If she’s going through a tough time, you need to show her how much you care and you’re worried. Seriously just talk to her as much as possible - basically, let her unload, so she knows she has a place to go when it gets really tough. Be sympathetic and accepting and let her know how important she is to you and that you’re there for her no matter what. If you can, try to help with the source of her problems, anything specific that’s making things hard for her right now. Since she’s pretty popular on the site, remind her how much she’s appreciated on here, because I’m sure we do appreciate and love her. I can’t imagine if anyone I know in the Tumblr community killed themselves, no one that wouldn’t be sorely missed. Tell her that there a lot of people here ready to help her and listen to her, because we are. If you think she’s becoming really serious about it, ask her directly about it definitely get outside/medical help.