She probably just totalled up her cat food, vet bills, and other cat expenditures to arrive at that total. Animals are surprisingly expensive to keep - my cat has cost me $2500 in vet bills alone in the last 18 months. A "replacement" cat is likely to incur similar (to her old cat's) vetrinary expense, so that is a reasonable assumption of replacement value, in addition to the purchase/importation value of the cat. The idea of this kind of lawsuit is to have your loss due to the other party's negligence be "made whole", in other words, all the money you spent on the item of property to enhance its value or to maintain its value must be taken into account when determining the actual "replacement price".
It was the same with my recent car crash case - the amount we asked for was based upon replacement value of the car as determined by the fair market price of an identical-model, similar-condition vehicle plus all of the (documented) modifications made to it. My lawyer's fees were taken into account. Also, the loss of use of the vehicle was taken into account (x dollars per day vehicle was not operational due to negligent idiot, etc, etc.). As in this case, the other party, an insurance company, did not show up. Oh well, their loss, I got what I wanted and the award was certainly reasonable.
I don't see that $45K is an irrational award with my cat-owning and legal system experience.
I disagree with that definition of replacement value (while acknowledging that it may be a legally correct one). The vet bills, cat food and other routine expenses would have been incurred with either the old cat or a new one. They are not additional expenses precipitated by the loss of the old cat.
Likewise, if someone totals my car, I expect enough money to buy a new one (including inflation, etc.), but I don't expect money to pay for my gas, oil changes, tuneups, etc., because those are expenses I would have had anyway.