Not quite. There are a few issues: Grammar: 'Surgery' is uncountable, so there should be no article in your sentence. You can say 'an operation', but not 'a surgery'. Register: 'Underwent' is technically correct, but it's a word rarely used in everyday English. It's rather formal and over-precise. We tend to use the all-purpose verb 'have', as in 'to have surgery' or 'to have an operation'. The meaning is in the noun, so we don't need a more precise word for the verb. Terminology: The adjective from 'spine' is 'spinal', so you could say 'spinal hernia'. In everyday conversation, you'd probably just say 'spinal surgery' . I believe the medical term is 'herniated disc', or, to be more exact, 'lumber herniated disc'. So if you wanted wanted to be clear about the type of spinal surgery, you'd say 'My friend's aunt had herniated disc surgery.'

That sentence is correct. Another way to say it would be. "My friend's aunt had spinal surgery."

SuKi's answered is excellent. I will point out that at least in the U.S. "surgery " is a countable or uncountable noun. We often say "he had multiple surgeries on his legs' though we wouldn't say "he had a surgery" but just "he had surgery" if only one procedure were performed.