Dental problems are common in rabbits, and you are right that they should be dealt with asap, before they develop into really bad problems. A dental burr to remove spurs is usually a quick affair, the bun isn’t under for a long time.

4 years is not old, but rather a typical age when dental problems start to occur. Some vets prefer to do bloodwork before putting a bun under, to check liver function (important for the ability to cope with anesthesia) and to see so there’s no active infection of any kind. The bun should  preferably not be overweight. For a healthy 4-year old bun, anesthesia is very safe, but the risk is, as you know, never zero. You should ask for painmeds (metacam) to give for a few days post burring, the buns gums can be sore for a little while. If the bun refuses to eat you might have to syringe feed her recovery food or pellet mush (pellets soaked in water).

The only thing you can do at home to try and prevent molar spurs from forming is make sure that the bun eats lots of hay. If you have access to clean grass (pesticide free, and not from an area with a lot of wildlife, like racoons), grass will be just as good as hay for grinding down teeth. (Start with smalk portions if your bun isnt used to getting fresh grass). A variety of hays helps keeping the bun interested in eating hay.

(I removed your GoFundMe link, we don’t allow members to ask for money on these forums).