I've never worn bibs. 80 miles in decent shorts under a skirt or regular loose shorts is okay for me. 'light touring' with an infrequent cyclist (50miles every other day but quite hilly) I did without cycling specific stuff just normal shorts but you would want to be carrying padded stuff in case that didn't work out. I would suggest making sure the set up of the bike is as comfortable as possible (body/arm reach as well as hand reach and weight distribution) is more important - and an appropriate saddle. The women's specific Specialized ones start quite cheap and suit me well, you might want to check out the women's saddle thread on here somewhere.
I've never worn bibs. 80 miles in decent shorts under a skirt or regular loose shorts is okay for me. 'light touring' with an infrequent cyclist (50miles every other day but quite hilly) I did without cycling specific stuff just normal shorts but you would want to be carrying padded stuff in case that didn't work out. I would suggest making sure the set up of the bike is as comfortable as possible (body/arm reach as well as hand reach and weight distribution) is more important - and an appropriate saddle. The women's specific Specialized ones start quite cheap and suit me well, you might want to check out the women's saddle thread on here somewhere.
also - 56km tt - srzly?!