If your wife tells you (perhaps while suitably liquored up, as you say, and per my suggestion above) that she masturbates and brings herself to orgasm in that way, it will mean half of your joint problem is solved. I.e., it will mean there's no physical or chemical reason she can't cum; rather, she just can't cum during sex with you.
In any case, I suggest considering your first sentence further. (This should have been my first suggestion.)
whitewife696969 said:
My sexy white wife in her late 50's has to take a narcotic for pain over the past year and she thinks it prevents her from cumming, at least with me.
Your wife's use of a narcotic-based pain reliever on a daily basis (presumably) for the past year implies she has an underlying medical problem that's causing her chronic pain. Pain relievers generally only last around several hours, but no M.D. would prescribe such a med every 3 hours every day because the patient would become habituated (become accustomed to it, so it would cease to be effective), then... worse still... would become addicted. This implies your wife probably spends much of her time on a daily basis, and possibly at night as well, in chronic pain.
Chronic pain reduces a person's interest in sex, in an overall sense. In the case of your wife, it may also be the cause of her inability to orgasm.
Also, since your wife is in her upper fifties that implies, of course, she's post-menopausal. A fairly large percentage of women, including those who were sexually active when they were younger, lose their interest in sex pretty much completely after menopause. (Some don't, however. Apparently there's a lot of variability among individual women.) Being post-menopausal usually results in reduced vaginal lubrication when sexually aroused; thus, intercourse tends to be painful for such women even when a lot of lubrication is used. This, conceivably, could be the cause of your wife's inability to orgasm during sex with you. (However, one might think your cunnilingus efforts, if you've been going about it properly, would tend to circumvent this problem.)
Given all of the above, if your wife simply wants to take a lover, she should tell you that. Perhaps you could entice her into doing so (or alternatively, entice her into admitting she doesn't think that would help) during the same seductive conversation, in a romantic setting, when you ask her if she masturbates and, if she does, whether she is able to bring herself to orgasm in that way.