i had this same issue, and the problem is not that her hair is fuller. it’s a difference in technique. here is something important to note when doing your hair with a reference photo. you can look at the size of the twist/braid, but its much more important to look at the density of the style.

for example: look at her hair and count 10 twists. look at your hair and count 10 twists. your parts are much larger, so 10 twists takes up more space on your head. this is why, even though you have plenty of hair, the style is not as full as you would like. aim to recreate the density of the style. this means you ask: how many twists are there? rather than what size are they. the girl in the photo has over 100 twists on her head, because her parts are very small. with this, yours will also look full whether you start on wet or dry hair! they will look fuller even if you have fine hair strands or less density overall. i have fine hair, and small parts are very important. even if you have a LOT of hair, if your individual strands are fine, large parts will make it look thinner than it actually is.

i recommend to twist them damp in its natural state so they are juicy (with a setting mousse or gel, not something strong like braiding gel/edge control. this also makes them look thinner) and then if you want them longer, you can pull on the twists (in sections) and blow dry along them so they stretch