Hi Greg.
I see a pot, and you said "plenty of water from rain".
I hope the pot has big holes that aren't blocked by sitting on anything impermeable, or that open into a saucer, like some store-bought plants-in-pots.
I see every garden problem as "probably caused by poor drainage", so feel free to ignore this. But re-potting it might solve the problem even if it is NOT root-bound. It may be periodically root-drowning if the pot doesn't drain really fast after every rain.
1. You might just tip the pot sideways and try to lift the rootball enough to get a glance at it.
If all you see are roots tangled over and under more roots, trying to find ANY little scrap of soil to call their own, it may be pot-bound and needs to be potted-up and/or root-pruned.
If you see only few roots, skinny and short and slimy at the tips, in rather wet soil and no visible air gaps, the roots are probably drowning a little every time it rains. Discard the fine potting soil and repot into a much better-draining mix.
2. If you are reluctant to rip your wife's plant out of its pot and automatically become responsible for anything bad that happens subsequently, maybe just set the pot up on something porous or rough so that water can come out of the holes freely.
Set some wicking, water-absorbant fabric under the holes so that they press against he soil in the bottom of the pot (like an old towel or tee shirt or several cotton socks). Pressing against the soil is key. That "connects" the toweling to the soil, creating a continuous capillary run from the top of pot to the bottom, THROUGH the holes and INTO the toweling.
Now drape one end of the toweling DOWN so it dangles BELOW the bottom of the pot. Now you have a wick that will PULL water out of the pot, using gravity PLUS capillarity to keep that pot draining.
Maybe even protect it from heavy rain.
If it perks right up, it was probably the water-logged fine potting mix drowning the roots. You'll still have to re-pot it to get rid of the fine potting mix, but now it won't be "YOUR crazy experiment that killed MY plant". If your wife is convinced that it MUST be re-potted, it wouldn't be YOUR fault if you offered o help her out with HER project of re-potting HER plant, would it be?
But hey. I see EVERY problem as "probably bad drainage", so take it with a grain of salt.
{Edited to add:
I forgot to say: first, just pick up the pot in your hands. Does it seem almost as heavy as it would be if that pot were filled with water? If it seems that heavy, the soil probably is saturated with water, and the roots are trying to survive even though they are being held underwater for hours or days at a time, after rains.
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