You can't tell what her sexuality might be just because she likes some TV celebrity. You like some male TV celebrities...does that mean you want to be male? No, it doesn't. The fact that she thinks Ellen is cool doesn't say anything about sexuality. And what business is that of YOURS in the first place? None.
Sisters traditionally get engaged in trying to force each other to assume a certain role, for their own, respective purposes. They do the same thing with their mothers, and their mothers do it back to them. It all turns out to be a complete (and I mean COMPLETE) waste of their time and effort. Your sister will be whatever she will be, and you can't mold that to suit you - and unless she's thinking about being a drug addict or a sex slave, you shouldn't be poking your nose into her process of growing up, while YOU have your OWN growing up to do.