Hi, I'm Dr. Bonk. This is very exciting for you and Bella. The first thing is you'll want to do is start feeding her kitten food within the next week. This provides much needed calories. Also provide her with a nesting box somewhere quiet, warm, and where she feels safe and protected. Some cats will stop eating prior to delivery while others will have an increased appetite. Both can be signs that the time is near.
When she starts labor, it is best to take a backseat and don't over crowd her. This can make her uncomfortable and want to find a new spot.
Most deliveries occur easily without any assistance, but if you notice the mother in hard labor, lots of straining or vocalizing, for an hour without producing a kitten, you should get her to a vet.
Kittens can come out head first or butt first. Both are normal and no problem unless the mother is tired. It can be several hours between when the first kitten and the last kitten are born, but there shouldn't be several hours between one kitten to the next. This would be another sign that she needs to get to a vet.
Some things to have on hand:
fresh bedding-to change the bedding after delivery is complete
rice bags or warm water bottles (not heating pads)-to warm up sluggish or slow kittens
clean towels-to rub and invigorate sluggish or slow kittens
Bella is going to do all the work and most of the time labor and delivery happen without us even being aware. If it comes to the point of having to help her, it is best to be in touch with your veterinarian. I hope this helps. Thank you and good luck!