"Her class is so much fun." This means that you "enjoy her class". The important thing to note here is that "fun" and "funny" are not synonymous in meaning (they don't mean exactly the same thing). Something that is "funny" generally makes you laugh or smile and is not very serious; a joke or a comedic movie would be a good example. Something that is "fun" may make you laugh or smile, but things that don't do that can also be "fun"; for example, going to an art museum may be fun (enjoyable), but it may not make you laugh or smile. These are very generic ways of explaining the differences between the two words, but it should help.

Michelle is right. Furthermore, 'fun' (in the context of your sentence) means: "pleasant for oneself." Whereas 'funny' means: "amusing (to you and possibly others)." Example: "Studying Japanese is fun, but not funny." Oh, and you can't say "much funny". That would have to be "very funny." But, conversely, you DO say "much fun" and NOT "very fun". So. "Her class is so very funny" -> Her class is full of funny people, "Her class is so much fun" -> Her class is very enjoyable to take.

funny着重于滑稽好笑 fun 着重于好玩 有趣