Yes ran it by the vet and got the ok.
Introduced them individually and no problem.
She doesn't seem to have any allergies or sensitivities.
I think the constipation/hard stool is the vet food and
the increased amount she is eating.
Will see vet on Monday and see if her weight has stabilized or if she lost a bit again.
Either way, I plan to stop the vet canned food and switch with a good high end canned food that meets the same requirements.