Quakers 'seem' like easy, small birds upon looking at them, but they are an extremely complex species when mature. They are also a species known to pluck more easily than some. One of the first things I'd do, is get this bird SEXED. The vet can do it and send in the test, or you can do it yourself for a very reasonable price with a simple kit by Avian Biotech Avianbiotech.com - Avian Sexing Center
(reputable company worldwide). It's important for several reasons (this is one) to know whether you have a mature female or male. Perhaps this is hormonally related, and different considerations will need to be taken for a female.
There are a ton of reasons a bird will start plucking. From hormonal, to medical, to behavioral. I agree with Deborah, that your mom first needs to take her bird to an Avian Specialist vet to get to try to get to the bottom of it since it just started. An avian specialist, not just one 'who will see birds'. Also, make sure the bird has sufficient stimulation in her environment. Quakers in particular often demonstrate a personality in terms of intelligence and tenaciousness which is often akin to much larger birds, as well as a high activity level. Without the proper stimulation, this 'can' lead to frustration and self mutilation, and striking out. Some good items are shreddable and preenable toys, especially ones designed for pluckers, chew toys, "smart" toys where the bird has to figure out a puzzle, etc. and enough of them. Also, if your mom isn't familiar with training methods, I'd suggest her googling "positive reinforcement" training articles online, as there are a ton of them. Sounds like the bird can also benefit from training to keep her stimulated, and her mind off "other" things. Also fun and challenging for her and your mom to bond in a new way. My Safe Bird Store | Discounted Bird Products | BIRD FREE ENVIRONMENT| Free Shipping Available
is an excellent source for bird toys and products. Good luck!