Hi Cuma eksen,
It depends on how much of her sister coming along to these dates you can tolerate.
You should probably try to find out from this girl about whether her sister will stop coming to these dates at a certain number of dates.
If you find out that she will, perhaps, you can hold out until then.
However, if there is no seeming end to her sister coming to the dates, it may not be worth it to keep talking to this girl.
She may have called you her BFF, but that doesn’t mean that she only sees you as her best friend.
She does like you romantically.
After the first date, she texted you and let you know that she had a great time and wanted to know when she would see you again.
She has made good eye contact with you even though she is shy and tends to look away relatively quickly before bringing it back.
She laughs at every joke that you make, even the ones that you believe are stupid.
These are all strong signs of romantic interest.
Calling you her BFF may just be an indication of her inexperience when it comes to dating.
Being that she has been raised in a strict catholic family, she may have been taught that she has to be able to like and trust a guy as her friend first before considering him as a romantic prospect.