Stop worrying, and just throw her a short text to see what's new with her.
It depends a tiny bit though.. were you chasing her? Or, did you two have a thing goin' on?
If you two were intimate, or you KNOW that she liked you and things just didn't quite work out.. you can afford to be a bit warmer. "Hey you

". Otherwise, a bit colder would be better just to see if she's available. "how've you been, ___?" would be a more neutral text to just see what's up, and then you can try to make plans. If you're usually suave, or you have been with her, then you can just skip the greeting and just go straight into asking her out ("Hey love, been awhile. Let's meet up").
She'll respond if she's interested, and unless she's nervous / just being nice, she will make time for you when you try to make plans.
If not, oh well. Just meet more women, and forget about her. I get texts from old flames in other states who end up being in town, of which I haven't heard the likes of in a year or two. When that happens I just go straight into my normal stuff: "Are you in town? We should hangout".
You need not be nervous: Texting is just a tool to make plans, not one to make her like you.