You may find this info helpful :
https://www.uhcw.nhs.uk/download/clientfiles/files/Patient%20Information%20Leaflets/Clinical%20Support%20Services/Dietetics/Paediatrics%20-%20How%20to%20gain%20weight%20in%20babies.pdf

If she’s eating plenty and steadily gaining weight, she’s just fine. Some babies are just petite

As long as she’s eating 3 healthy meals a day and eating enough. As long as she’s healthy and happy, there’s nothing to worry about. You may just have a petite baby, she’ll thank you for it later

My kids are thin they eat all day but it’s just their genes

unless she is dropping off her growth pattern or failing to thrive, you have nothing to worry about, she is totally normal! Speak to your GP or Paed and see what they say.
Just keep an eye on her growth chart and weight regularly,

sometimes they are healthy thin, i would check if her weight is in the right range first

Is she healthy? What does your midwife or doctor say? My daughter has always been thin and tall, as long as she is healthy don’t worry.

As long as she is healthy! Mine was quite skinny at that age – she has only just started to plump out a bit at 3. If you are worried check with the maternal health nurse, but otherwise things like breads and pasta might help.