Aw, is this Mama? I'm sorry about the tail injury. I hope it isn't as awful as the one my stray had.
If she's not peeing, that's worrisome. If it's a pooping issue, you could try adding some Miralax - start with 1/8 tsp dissolved in a little water and mixed into food. It has no smell or taste - even Celia never fussed.
Torbutrol may not cause constipation issues in the same way as a full opioid. But if you suspect it is (or maybe even if you don't), you might ask the vet about switching to buprenorphine, which is far more commonly prescribed, and seems to be the most effective pain med for kitties (the fact that Marie's Cali got that post-amputation says a lot!). We were always afraid to use bup with Celia because of her constipation issues, but when we finally did towards the end, it actually made her stool very soft. And I could have kicked myself for not trying it earlier...
It doesn't seem like Torbutrol is generally prescribed for long-term. This is from the World Small Animal Veterinary Association World Congress Proceedings, 2007. Maybe things have changed since then, but bup was recommended:
Butorphanol: The efficacy of the oral formulation for treating pain has not been evaluated...For the injectable form, efficacy is of short duration and limited to mild pain. Because of the short duration of action observed from injections of butorphanol, analgesic effects from an immediate-release oral tablet are expected to have limited effectiveness.
Buprenorphine (Buprenex): In animals it is reported that the duration of analgesia is longer (for example 6-8 hours) compared to the duration of action of morphine...In cats, buprenorphine was injected at a dose of 0.01 mg/kg with a duration of action between 4 and 12 hours...The oral (sublingual) dose for cats is 0.066 mL per kg (Robertson et al. 2003). Absorption was complete with plasma concentrations as high as the analgesic levels observed from injections.