There are surely several factors.
One is she shall have aplenty to drink, not to risk dehydration. Use a water fountain for cats if necessary.
She shall be unstressed.
Good food of course (what are you using?), of the type kitten food. As much as she needs and wants.
Do she eats and manage usually diary products like youghourt, cheese, low lactose milk?
These milk products shouldnt be necessary if she has good enough food, but in border cases they may be useful, both water, animal proteins and fats, and much calcium.
If she has problems with milk products, goat milk is useful. Does have lactose but seems to work beautifully for cats anyway.
If you dont have problems with salomonella in eggs in your country, try with eggs yolk, ie the yellow of raw eggs - these are nice and verry useful nourishment.
There are also pastes with vitamines of type Nutrical (I think). Shouldnt be necessary in normal cases, but here perhaps...
Let others fill in!
ps. Are you a breeder? If not, please consider to spay her at least when they kittens are weaned.