Hello cat lovers !

I have a question regarding wet/dry food as it pertains to my
13 year old long hair tabby cat, who has alot of maine coon traits.

I have been feeding her dry food all her life, 1st IAMS then switched
to Eukanuba when it came out several years ago... Last year when
I brought her in for her annual checkup (she is doing just fine) the vet
suggested I may want to feed her some wet food along with the dry..
Anyway when I did this she ate it but within an hour or so she threw
it up... Well I kept this up for about a week and more than half of the
time she didnt keep it down... I tried different brands/flavors but that
didnt seem to be the issue so I just went back to dry food... I did buy
the best brands available at our pet store. I give her daily vitamins
(Well-tabs) to assist her nutrition , she loves them....

So my question ... what would be the benefits of mixing wet & dry foods
for her? Is it because of her age or is wet food more nutritional?
Is it possible that because for 12+ years I have been giving her dry
food that her stomach/digestive system finds wet food too rich?

I'll tell you what she has no problems with tuna fish from the can :)
Certainly cant use an electric can opener in our house without her
charging into the kitchen :)

Thanks!