Gaining muscle for female petite body type

If you have the training part in check then you just need to eat more.

You shouldn’t just be consuming protein shakes on training days. You want to hit your protein goal everyday.

If you struggle to eat enough calories then make smoothies. Add things like full fat milk, porridge oats, banana, peanut butter, scoop of whey and maybe a drop of honey. You can make really high calorie drinks if you feel you can’t force anymore food down.

If drinking calories doesn’t appeal then fats have 9 calories per gram so take a spoon full of peanut butter every time you walk through the kitchen. Drizzle olive oil on salads. Eat a handful of nuts.

Being consistent with calories and manipulating your intake is the key to gaining or losing weight.

BCAAs are pretty much useless, whey protein would be a far better choice and agree with Tic78 - hit your protein goal every day not just on training days. Muscle protein synthesis and breakdown are happening 7 days a week not just on training days.

Meal replacement shakes (but not actually replacing a meal) could be a decent option if you're not noticing any gains. Having protein shakes on days when you aren't doing strength work and on strength days may help too just to keep that protein intake higher. If you don't mind having two types you could do whey protein shakes after a strength workout and then use a casein protein powder at night before bed.