My thoughts on this is to give them separately, or mixing the zantac with the CCif need but giving the loxicom separate later. The zantac has 2 functions. It protects the lining of the gut but it also aids in gut motility. Loxicom (metacam) is normally advised to be given with or after food because it can irritate lining of the stomach and lead to ulcers. This is more of a risk for rabbits on long-term loxicom/metacam. The zantac you were given will protect against that anyway.
Im always worried they wouldn’t be getting the full dose if it mix with food. Especially if having to “force feed”. That’s just me though. If it’s a struggle to get any med in and mixing with food is the only way, then getting some in is better then none!
Is your rabbit liking the zantac okay? Is it the clear, liquid with strong peppermint flavour?
Is she eating CC on her own or do you have to syringe feed it? Is she eating some of her normal foods on her own?