Hello Gillian, I'm Dr. Deb and will do my best to help you today.
I'm sorry that Chrissy has been diagnosed with liver issues especially since she's so young.
When it comes to diet in these cases, I don't typically recommend or suggest a diet restricted in protein unless my patient demonstrates evidence of protein intolerance (such as in end-stage liver disease or those with liver shunts).
Most good quality dog foods will suffice just avoid those high in fiber.
It sounds as if her diet is not quite as balanced as it should be if she's only being fed chicken and rice. But I understand the limitations and difficulties involved in getting some dogs to eat so at least a daily, multi-vitamin supplement should be added.
In terms of medications/supplements, the following are what I typically suggest:
1. Over the counter Famotidine (at least it's available here in the States) which can help with nausea issues although Cerenia is also a very potent anti-vomiting drug (which would have to be dispensed by your mom's vet if availalbe in Spain.). The dose of Famotidine, though, would be 1/4th mg/lb twice a day about 30 minutes prior to a meal. For example, a 10-15 lb dog would be given 1/2 of a 10 mg tablet at one time.
Another option would be Omeprazole at a dose of 1/2 of a 10 mg tablet once a day.
2. Vitamin E--d-Alpha-tocopherol (not d-l) at a dose of 10 IU/kg/day
3 SAMe (S-adenosyl-methionine) at a dose of 10 mg/lb once daily
4. Milk Thistle (Silymarin) 20–50 mg/kg per day
#3 and #4 can be purchased as human supplements but they are combined in one veterinary product called Denamarin. I'm not certain if Denamarin is available in Spain either but it's not a drug so shouldn't require a prescription.
5. Many dogs with liver disease will benefit from antibiotics since bacterial colonization can easily take place. If she's not already taking them, Clavamox, Cephalosporin or Metronidazole are good choices. I usually prescribe them for several weeks.
6. I might consider Ursodiol because it not only increases bile acid flow but also has been shown to reduce hepatocellular inflammation and fibrosis. Again, this is a drug most commonly prescribed by a vet and is not available over the counter.
I do understand that it can be problematic in some cases to try and administer so many medications to a dog at one time, though.
I hope this helps. Deb