I hope I'm posting this in the right section. If not, please move the thread and accept my apologies.

So I met this girl a while ago, we didn't have the opportunity to meet as a pair yet but we did the best we could and chat over the phone. Yesterday we've talked about one hour and a half. I tried to do some teasing, make her laugh and make her feel great and it seemed like she really enjoyed it.
Now she texted me to call because she was out of minutes but she only wanted to swap just a few words. She said, however, something like
"Let me tell you something! My sister is crazy about you!"

Well, I got the idea from her sister in person a while ago, but she is definitely not my type (ill-tempered, stupid, fat, etc.). The problem is, I really don't know how to interpret this. Does this mean that she is not attracted by me and sees me better of with her sister? Should I feel great because someone closest to her likes me so much and does that make me more attractive towards her? I know it would be a logical deduction, but I don't seem to get it (don't know why!).

Moreover, if you were in my shoes (feeling something for her but nothing more than repugnance for her sister) what would you do? What would you say to her and how would you act?

Yeah, it probably means that she thinks you'd be great for her sister, and hasn't thought about you two being together. You need to introduce that thought bluntly. Subtle hints probably won't work here.

I'd say something like:
"That's great, but I'm not crazy about your sister... I like you."

If she's still wanting to see you with her sister, it doesn't mean she's not interested, she may be interested, but all the same nothing will happen because she doesn't want to upset her sister. Tough call. Good luck, man!

Prince, is absolutely correct.

You need to make your choice and deal with the consequences.

Make it clear to her that while you're flattered by her sister's interest in you, you won't be able to reciprocate that because you're attracted to her. And if she tries to sell her sister to you, tell her "I don't know. Maybe it's how I am, but you're selling too hard. I already told you what I want. I stick to my decisions." and have a calm smile while telling her that.

If she likes you back, she won't care. Because somewhere deep down even she knows how her sister must look like.

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" You're born alone and you die alone and this world just drops a bunch of rules on top of you to make you forget those facts. But I never forget. I'm living like there's no tomorrow, because there isn't one. "