When a doctor chooses to treat a finger joint with a splint, the goal is usually to help relieve the pain and protect the joint during a painful flare-up. As you say, some splints are awkward, even bulky, and can make it difficult to do every day tasks. What often happens is the patients end up taking off the splints, therefore not benefitting from them.
There are newer splints that have been designed to help avoid this problem. They are generally made of plastic, are thinner and lightweight, and maybe most importantly, they don’t cover the fingertip. It may be best if your mother speaks to her doctor about trying alternate types of splints.