Yep thats me, the animal lover!
Safari park would be pretty awesome! Does she have a fav animal? You could make sure whichever you choose has that animal there aswell.
Looking at both they both look pretty good. The safari one doesn't give you a list of activitys but it does you a list of some animals, giraffes, elephants, lemurs, meerkats and lions that the activitys could involve.
The full experience day though gives you a full itinerary so you will know whether your sister will like it or not, only thing that puts me off with that one is handling the creepy crawlies, eeeeeeeeeeee lol. Also with that one you and you family could go along for less than a tenner each and see her helping out which would be really nice! And she will get a certificate, lunch & a tshirt, but it does cost abit more!
I think I saw a thing on lastminute.com for tiger tea where you get a tour & pass of the zoo for the day aswell as lunch in a glass room looking out on the tigers, if you think she would like that.
Good luck, I'm sure she will love whatever you choose!