If a person can no longer assimilate food (because their processes of digestion and absorption have shut down), or if feeding provides negligible nutritive benefit, but causes severe discomfort and pain (nausea, vomiting, infection or abcesses at the point of tube entry, risk of aspiration/suffocation) and death from an underlying cause is in any case imminent-- in these cases, futile, burdensome attempts to provide nutrients can be discontinued.
If such was your mother's case, then you had no need to continue attempted feeding, and you ought not to feel guilty.
Because I don't know anything about your mother's condition, that's all I have to say. I hope you may be at peace.
Thank you, Mrs. D. That was very kind of you.