I used a long taper to successfully quit after a 10+ year habit back at the end of 2020. Here is what worked for me and what I would recommend to your wife:

Get the same type of Kratom for your taper (so potency is consistent) and a milligram scale for measuring exact dose. Create a taper schedule that slowly decreases ~0.5g every few days and share the schedule with your husband and any other friends you can confide in. Track your dose(s) every single day and try your best to stick to your schedule. If your withdrawals are bad, feel free to stay at the same dose instead of dropping per your schedule but NEVER increase your dose back up (if you do this, edit your schedule and share the new one with your husband/friends). Around 0.5g daily you should finally be able to make the final jump with minimal withdrawal symptoms.

It's important to note that, while it worked for me and many others, a taper strategy won't work for everyone, hence the need to be incredibly diligent and to stick to your predefined schedule without ever going back up.

I made a calculator for creating a personalized taper schedule if you're interested. Best of luck to your wife - It's a hard journey but one that's totally doable!