The only way to ensure that your new kitten will never get FIP is to make sure she doesn't have the corona virus. Since probably around 90% of cats have corona your first step is to get a titer to confirm it's presence. BTW, you can have false negatives so a good rule of thumb to follow is to get at least two, or preferably three negative titers in a row.
Presuming that the titer is positive (usually a titer greater than 1:40 is considered positive, although some don't consider it positive unless it's greater than 1:100), and that she is an only kitten the best way to eliminate corona is to change litter and sterilize the litter box and pooper scooper with bleach every time she has a bowel movement, or at least daily - that way she cannot keep reinfecting herself. This is a lot of work, and can obviously be expensive going through litter like that, and if you have more than one cat you need to quarantine each and do the same thing, otherwise they will keep infecting each other. Most cats will eventually shed the corona virus it they do not keep getting reinfected from themselves, or other cats, but about 13% of cats will remain lifelong carriers. That's not to mean that they will convert to FIP - that is an entirely different matter. Since it is not yet completely understood why cats with corona virus convert to FIP (although research is making strides in this area) there is no known way to prevent it from happening if your kitten happens to be one that is susceptible to it.
Some of the things that seem to trigger the conversion to FIP is stress (e.g., the stress of moving to a new home), illness, very young or very old cats, and having a genetic predisposition. The only things you can really impact on this list are stress and illness, and that would be hard since the simple act of bringing her home will cause her stress, and stress can trigger illness. You will need to do your best to help her transition smoothly and easily into your home (there are other threads on bringing home a new kitten on this forum that you can read). You can prevent illness also by avoiding future stressful events, and not allowing her to interact with other cats - easy if she is an only cat.
