That is why RIGs are now usually recommended -- to avoid general anesthesia, reduce procedure time, and make it easier to use BiPAP throughout the procedure, among other things.
Once someone's swallowing is significantly impaired, which I presume your mom's is if she is using an NG tube, the sooner a feeding tube is placed, the greater capacity for recovery from the procedure there can be because as you say, she will continue to lose muscle and mobility.
Most PALS if it is placed in a timely fashion recover well and can tolerate tube feeding, preferably with blended real food or a real food formula such as Whole Story.