To be fair, we'll have to wait and see on the future part- we don't know how big Fiona is going to get. If she stays her current size, absolutely she shouldn't, but if she grows to be closer to the full-grown size she should be, I don't know why it wouldn't be advisable to breed her in the future.
Fiona is almost 6 years old now and still is very small. I think the chances of her getting close to normal size is unlikely.
Irregardless, it's concerning that the zoo advertised Tucker trying to breed Fiona- as it makes you wonder what plans they have in store for them, even if Fiona is contracepted at the moment.
Worth bearing in mind Fritz was conceived while Bibi was on contraception - supposedly anyways. The question is when will Cincy's management come to their senses, before or after they destroy the zoo's cash cow... The exhibit is sized for two, it now has four and may go to five...