I have to disagree that things were that different for women 19 years ago. That was 1998, not 1958 for heaven's sake!!
Women in their 50's were just as capable at taking care of themselves 20 years ago as they are today. I recently turned 60 & have many relatives & friends in their late 60s, their 70s & 80s. In fact, I think I only know 1 woman younger than 80 that has never worked outside the home. I can't even imagine being 54 & needing to move in with my children after a spouse passed. I also know many such women who were widowed in their 50's or 60's & not 1 did anything like that. Everyone of them moved forward with their lives & maintained independence until their own health failed.
OP, I think you made a mistake taking her in back then. Possibly out of guilt, possibly to help with your kids or who knows why. But I think you created this by never addressing the future & treating her like some fragile creature who couldn't function on her own. And unfortunately, now at 74, she may actually not be able to be independent much longer. Disabling health issues can come up at any time at that age. Or they may never come. So you moved her in when she really didn't need to be there. And now when she really might start to need help for real, she has to be out on her own. Makes no sense to me.
IMHO, this is a family issue. You should now engage both your mom & siblings in creating a plan for her future. You are certainly entitled to move on with your life. But that doesn't really entitle you to throw your mom's life into chaos & dictate her future either.