' puellae' is pronounced /pʊ'ɛl.leə/. It's not just me haiving an opinion, check Wiktionary for the pronunciation of the singular form
Ok, thanks, but I think both our versions do not get it graphically correct that the sound is NOT a diphtong, whereas in the audio recording behind this sentence it is. That was my point.
'ae' is almost always a diphtong, and is pronounced as the 'ai' in English 'aisle'.
In loanwords (usually Greek) it may be pronounced as two syllables, but then you would normally write 'aë' for clarity. Ex. 'aër' (air).
Bennett' New Latin Grammar gives a consise and full overview over Classical Latin phonology: http://www.thelatinlibrary.com/bennett.html#sect3
Look under 'sounds, accents, quantity'.