I was wondering whether anyone knows the Proto-Indo-European equivalent of the Greek suffixes -ina (-ίνα) or -issa (-ισσα), or whether PIE has any different feminising suffixes that work similarly?
The main PIE feminine derivational suffix was -ih2: compare *deiu-o- 'god' with *deiu-ih2 'goddess' (Skt. devī).
Incidentally, this suffix is actually the indirect source of the Greek suffix -ssa: when added to a stem ending in -t or -k, you get e.g. *melit - *melit-ih2, which becomes in Greek *melitya and then melissa (Attic melitta). From cases like these the suffix was reinterpreted as being -ssa and extended to other types of stems (e.g. basilissa 'queen').
The feminine suffix in PIE is believed to be -i̯ea̯, though the ablaut grade in nominative is not certain. Traditionally reconstructed as -i̯ea̯ (because of long vowels in Latin), but Beekes hypothesizes that the Nominative form was -ia̯, while in other cases it could become -i̯ea̯. A form -a̯/-ea̯ also can be seen in some words.
The suffix is believed to originate from the suffix -ia̯ for collective number.
Some reconstructed PIE words with the suffix include
a̯oldhia̯ a dugout boat
colia̯ hiding place, dug-out
ma̯eghu̯ia̯ young woman
neptia̯ nephew (fem)
pie̯u̯eria̯ fat woman
preu̯ia̯ lady, mistress
u̯eĝhia̯ track, road
- Most animals had feminine form
e̯ele̯nia̯ female elk
The suffix could be combined with other suffixes as well, to form constructs like -ikea̯/-ika̯/-ikia̯, -tria̯/-tra̯/-teria̯, -nia̯, -u̯ia̯ etc.