Mae hi'n gyffrous.
How would one tell or distinguish between excited and exciting if/when required?
There is a way. It's the difference between using the adjective above for 'exciting' ie
Mae hi'n gyffrous = She/It is exciting
and using the verb 'cyffroi' (or cynhyrfu)= to excite
Mae hi wedi (cael) ei chyffroi = She/It is excited (literally = She/It has had her/its excite)