Grandmother forcing to give formula

So I supplemented with formula until the first week since my milk hadn’t fully come in yet but after that i stopped since there was no need

My mom tho kept telling me it’s good to give atleast 1 bottle of formula a day for good weight gain which makes sense since formula fed babies do gain weight more quickly but I’m not concerned with rapid weight gain, i just want healthy weight gain.

My baby is 6 weeks now and gaining weight accordingly but is just really fussy and doesn’t easily settle after feeds and so she thinks I don’t have enough milk and need to give formula

She says I’m selfish in my want to EBF (since I hadn’t got to do that with my first) She says the baby’s health should come first always, and I know it always will, but there’s no solid reason she needs formula. I’m tired and feel discouraged all the time