Hi Gness - poor you, what an awful dilemma, I would hate to be in your position having to take decisions on your own, but guess I could well be in the near future as my Mum is also in her 90th year. She too has the constitution of an ox, and we are very fortunate that she still lives independently with no dementia.
May I suggest the problem may not be as bad as you think, my FIL started this problem of loose bowels when he was in his final years in a care home. Apparently it was like an incontinence and to put it crudely he was blocked up and leaked down the sides of the blockage. The doctor told us this often happens to elderly people because of their inactivity and poor diet (he just picked at his food in the care home but had eaten hearty dinners previously while living at home) and it wasn't causing him any physical distress just mentally as he thought he was very ill as he wasn't going to the toilet properly.
I do hope you and your family make the right decision but I tend to agree with you, your poor Mum doesn't seem to have much quality of life now and if she is saying she wants to go home to God, she perhaps understands that she can't get any better and maybe wants to join your father? Sending you my love, God bless x