Please can someone explain why these 2 sentences have different ways of saying she didn’t, i.e. one uses nag oedd… and the other bod hi ddim… Are they interchangeable, i.e. either way of saying it can be used?
“You’d tell me she didn’t want to go wouldn’t you?” is “Byddet ti’n dweud wrtha i nag oedd hi’n moyn mynd yn fyddet?” (01:58)
“You’d tell me she didn’t want to answer wouldn’t you?” is “Byddet ti’n dweud wrtha i bod hi ddim yn moyn ateb yn fyddet?” (04:39)
Hi, yes you are correct. Two ways of saying almost the same thing in the 2nd part of each of the sentences: That she didn’t.
The first sentence has the negative part at the start of the 2nd phrase nag oedd hi. literally: that not did she
The second sentence has it after the word for she. Bod hi (d)dim: That did she not.
Don’t worry too much about the seemingly different tenses. That’s how Welsh works.
Interestingly, someone has asked a similar question in the topic about Level 1 Challenge 22 
Diolch! 