I don't disagree with anyones advice about what pains in the bums pups can be to older dogs and would actually have agreed with all that has been said and tell you I thought it a bad idea too............... apart from the fact that a dear friend of mine who also has a Cav funnily enough with terrible heart problems and who basically had no get up and go in her at all went and got a pup!

I actually felt it unfair but when I called over to see her recently I just could not believe the change in her older Cav, she is alive again, she has been on the 'she's only got a few weeks left to live' list 3 times now, but each time pulls through, the pup has rejuevanated her she is slow and old but her tail is wagging to death and she somehow just looks younger.
In this case the pup has I feel saved her older dogs life literally and given her a reason to go on.
I'm not saying it would be the same in your case all dogs
are different but I will never be as rigid in my opinions, the two of them together are beautiful.
But, even so it depeneds on your girl if Rosie is a dogs dog she may well enjoy a pup, but if she is a total mummies girl who likes all the attention then allow her to have your full attention. :-)