It is something Cavaliers are very good at!! Resisting those big eyes is hard.
Make sure to pick a good quality dry food, or even perhaps consider a high quality raw diet such as Darlings - this is prepared especially for your dog, so you know it takes into account her needs.
http://darlingsrealdogfood.com/
If you are going for a dry food, something like Markus Muehle, James Wellbeloved, Fish4dogs, Burns are all good makes - sadly Bakers tends to be full of colouring and not much else!!
Once Tess is spayed you will probably find she will go the other way and eat anything!
I would highly recommend she is spayed, if you search on the forum you will see that it prevents all sorts of nasty health issues, and is much better to be done whilst she is young - some of these things can be fatal
If you are planning to breed from her, she would need to be a very good example of the breed, she would also need to be at least 2.5 years of age, with both parents over 5 and heart tested clear by a cardiologist, also both her and her parents should be MRI scanned, eye tested and ideally patella checked and x-rayed for hip dysplasia. Obviously this all applies to the stud dog too!
It is not as simple as just putting two dogs together, they could easily hurt each other, especially if neither of them have been mated previously.
Whelpilng can be very difficult and expensive if you need vet treatment, and sadly there is the possibility of losing both your bitch and the puppies.
Breeders who do things properly rarely make money out of a litter.
ALl good reasons for having your animals spayed or neutered.