I also recommend the topics that Romy linked, as they immediately give you some things to try and think about regarding that topic. Another, but much more time consuming, would be to read the beginnings of the diaries. The real gems are hidden there
Your question is a very fundamental one and as such it goes deep into everything that builds up relationship with the horse. I'd say it depends very much on the horse and her previous experience with humans. It can be a very lengthy process to develop a bond with a horse that is stronger than food on the ground. And that is already the core of it: you basically have to be more interesting than the food. You cannot force the attention, otherwise you won't have an open, curious attention next time, but a very avoiding one.
Luckily, horses are very curious and social by nature, so that can play into your hand if you wait for the horse to become interested on her own. It might be harder with school horses, or horses trained with a lot of negative reinforcement, but basically it's a matter of time and creativity on your side. If you are in the arena you can try to get her attention by focusing intensely on something like running in circles, doing hops, side passes or flying lead changes (Mucki likes that for example). It has to be something that you do with genuine fun and with focus. Ideally you should be able to forget the horse in the process. Especially with young horses like your Bella, the chances are good that they get drawn in by that kind of genuine playfulness.
Of course you could also try objects like balls or something, but for some horses they are just scary at first.
What is almost as important for me is to establish a way of communicating with the horse that is understandable and above all: rewarding. If my presence is rewarding to the horse, it will seek me out. Simple, isn't it?
Like a good friend with whom I like to chat for hours, because it just feels mutually good.
If you answer basically every reaction (at first) to you with a positive reward (food works best here), you will soon get a very interested horse that will love to interact with you.
Then comes the matter of food manners, but that's another topic