Thanks for your question regarding your Rough Collie girl Gael who has been lethargic, vomiting and breathing quickly and then slowly throughout the day today. These symptoms are definitely a real concern in an older Collie, and could be associated with anything from acute gastroenteritis, to an internal organ issue, to a bleed within her abdomen, or even just as a pain response from another cause. Given her age - you really are going to have to keep a close eye on her this evening. If you can get her seen by your local Vet or after hours Vet now, then this really would be the safest bet given her age. As she has had vomiting, then you are best to with hold her food now until the morning and then start her on something bland from tomorrow. Cooked, boneless skinless chicken breast and white rice is ideal for this. Right now you need to make sure she has ample access to fresh water and that she is drinking it. If she can't even keep water down, she will quickly become dehydrated, which would be another reason to get her seen tonight.
For now, please continue to keep a close eye on her. In particular, please keep a close eye on her mucus membranes, capillary refill time and respiratory rate tonight as follows:
Mucus membranes - flip her lip and look at the color of her gums. They should maintain a nice salmon pink color. Get her to the emergency Vet if they appeal white or very pale pink, or if they are a dark deep red color.
Capillary Refill time - this measures blood perfusion and test this by putting your thumb on her gum to apply pressure. After you release your thumb you will see the gum blanch. Capillary refill time is the amount of time it takes (in seconds) for the gum to return to a healthy pink color from the blanced white color. If 2 seconds or less don't worry - if it is taking significantly more time, again - off to the emergency Vet.
Respiratory Rate - if she is continuously panting throughout the night this is a sign of shock and or pain and a signal for a trip to the emergency Vet. If she is just panting every now and then, this isn't as much of a worry, but if you think she is having difficulty breathing or seems distressed, then you need to get her seen straight away.
It is always better to play it safe in these situations, so do get her seen if she doesn't settle down soon won't you. Best of luck with Gael and please keep in touch with her progress if you get a chance.