It would probably be better to just wait until she discusses relationships one day, then playfully segue into that topic. But until it gets brought up casually and naturally, forcing the subject awkwardly is just asking for friends-zoning (IMHO.)
Maybe there is the chance she feels the same way, but you had better read into things first by understanding her views on relationships in general. Either way, breaching the topic through correspondence is a lot easier than through face-to-face conversation or even through a phone call, but it's also a lot easier to be summarily rejected also. Having the conversation on the phone or in person will let you pick up a lot more cues to warn you about your chances. :/