The bottle was covered with stickers saying 'if ingested seek medical advice immediately' in umpteen languages, so I called 101 for emergency services and ended up getting both police (who I hadn't asked for, but who may have been having a boring Sunday morning and in need of some excitement) and an ambulance.
B., who like many autistic people generally prefers her own company, took it all in her stride and greeted each new set of uniformed visitors with a big smile. She was of course unable to tell us how much of the chemical she had swigged, so it was off to the hospital we went, B. clearly somewhat thrilled by the ambulance ride.
Once there, the nice folks in casualty had a look at her and determined that the chemical in question was largely citric acid, so heavily concentrated that it has a pH of 1; if B. had had enough to do her any harm, she would not have been in such a sunny mood. So we went home relieved.
My sister had bought the stuff for her husband's photographic studio. He is colour-blind, so works only in black and white photography. Apparently the equivalent chemical in the process of developing colour photographs is much nastier. One should be thankful for small mercies.