As you want her opinion, why not ask her for that?
"What's you suggestion?" COULD be said in such a way that it offends, but this is a nuance of the speaker. Off-hand, dismissive etc.
BUT, if someone asked me the question in a pleasant tone, it would not offend.
You need to give further background, because the author could be using this type of question to sound sarcastic or moody, for example if I was trying to come up with an idea for a a group outing and you spoke out saying that you didn't want to go bowling because you hated being in crowded places (not a great example I know, but I can't think of anything else!) I could say, 'Well what's your idea then?'
This would make me sound as though I was offended at your reply because I thought I had a good idea, and you hadn't come up with a better one.