I'm trying to introduce bottle to my 7 week old LO. She seems to be taking it well but i still want to BF her. How often should i give her the bottle to ensure that she does not reject BF?

It really depends on the baby. I introduced bottles to my newborn very early and intentionally provided a large range of brands so she would still prefer the nipple. When she was 6 weeks old, she went on a total bottle strike and I had to latch her 100%. She only started taking the bottle again when she was 5 months old. Perhaps you could try a bottle similar to the nipple, like MAM or NUK latex. These two have very good reviews from BF moms.