It must be very reassuring that she likes the smoothies so much. At least you can be sure what food intake she is having and that it is nutritious.
Giving Penicillin injections to a rabbit is daunting, but I've done it for a few of my rabbits and you do get very used to it. I actually find it a lot less bother and a lot less stressful all round than trying to syringe liquid medication. And importantly it can be extremely effective. The only concern is that you must make sure that, if any drips on the rabbit's fur, you wipe it off immediately as they must not ingest it. I never found that to be a problem though.
Giving Penicillin injections to a rabbit is daunting, but I've done it for a few of my rabbits and you do get very used to it. I actually find it a lot less bother and a lot less stressful all round than trying to syringe liquid medication. And importantly it can be extremely effective. The only concern is that you must make sure that, if any drips on the rabbit's fur, you wipe it off immediately as they must not ingest it. I never found that to be a problem though.