The best way to ease into dating is by setting up some activities that you will both enjoy in and of themselves, rather than activities that hinge on your enjoying each other's company.
The most traditional "dates" (getting coffee, getting a meal together, etc.) are set up as opportunities to talk to each other. In your case, you may want to start one step back from that, though, since the two of you have never actually hung out in person and online interactions can be quite different from in-person ones.
Look for activities or events that appeal to your shared interests --- things you think both you and she would probably like to go to whether or not you were going together. For example, maybe going to a gaming tournament? Or seeing a movie* you know you're both interested in? Would she like doing a locked room puzzle with you and some friends, or playing paintball, or laser tag, or hiking? Check to see if an author you both like will be in town for a book signing, or if there's an exhibit at a local museum that would appeal to you, etc. You get the idea. No matter what, you should phrase the invitation as something that will happen with or without her, but you'd love her to join (e.g. "Hey, some friends and I are going to go hear Neil Gaiman when he's in town next week. I know you love his books --- wanna come?"). That makes it clear that you're not inviting her on an actual "date", just looking to hang out doing something fun with people you enjoy.
Here are the advantages of inviting her to a strongly activity-focused hangout rather than a conversation-focused one:
- It is less clearly a "date", which would take pressure off both of you. She might be more likely to accept an invitation to a non-date hangout; if she's not sure whether she's interested in you romantically or not, she may be leery of leading you on if she accepts an invitation to something that sounds like a date.
- No matter what you're doing, if you do an activity for a couple hours with her, you'll get a chance to get to know her a little better and see if you want to keep moving toward the dating stuff. You don't need to spend two hours in private conversation to start to know someone.
- Even if the two of you don't really "click" in person, there's a good chance you'll still have fun if you're doing an activity you both genuinely enjoy. That might take some of the awkwardness out of deciding to go back to "just friends" afterward if one or both of you don't want to date.
A good activity-focused hangout should have something for you both to "do" other than just talk, ideally it should have clear start and stop times, and it should be something you're both interested in for its own sake. Depending on the personalities of you and this girl, you may also want to make it an event with more people than just the two of you (invite her to something with your friends, or invite her to bring her friends along). Having more people there helps to clearly communicate that it's not a date, but it can backfire if she's the type of person who would be stressed/overwhelmed by meeting a bunch of people at once.
If you successfully set up a time for you to hangout like this, great. See how things feel and if you want to keep getting to know her better, keep inviting her to these low-stakes hangouts. As you both feel comfortable doing so, you can add more "private" time before or after (e.g. "Hey, there's a really neat-sounding exhibit at the museum right now. Wanna go? There's a cafe I like right by there, so we could stop and get lunch afterward, if you like." or "Awesome Band is playing at cafe on Friday. Wanna meet up at your work and walk over there together?"). In this way, you can slowly build up your in-person friendship. And eventually, if you both want to, you'll be able to make a smooth transition to more date-y dates.
*While a movie might work, it also has some "baggage" as a date activity, and she might interpret an invitation to a movie as implying that you'll do some snuggling etc. in the dark, which she (or you) may or may not be up for yet.
