Were you friends first?

So, I have been friends with a girl for around 1 year, until recently we have just hung out as friends, lots of same interests (only thing which I dont like about her is she smokes weed). But we share a similar outlook on life and she is a bundle of positive energy to be around!

The thing is over the last three or so weeks I have developed feelings for her more than friends, before now I have seen her as a younger sister almost (she is a year yonger), but when she had to isolate due to c19, I felt so so so gutted for her and it made me realise I had feelings.

should I tell her? she is single (well has a fwb), question is do friendships turn into relationships? she flirts with me sometimes but always thought that was banter. She even showed me an outfit she bought for her fwb, a little rubber number, she was not wearing it obv.

You could tell her but in actuality she's unlikely to reciprocate the feelings you have for her. It will simply make things awkward between you, and the longer you are friends with someone else the less likely you would be together as the bond becomes more like that of siblings (Or at least it would feel like that for her).

but how do i know, If you started off as friends and it went into a relartinship how did you approach it?