If none of the other email recipients are in your contacts list or are completely unknown and unrecognisable to you, then it’s unlikely that you’ve been hacked.
Depending on how you’re accessing your email, you maybe able to hover the mouse cursor over the sender’s name to see if it is definitely from her and not just a label showing “missananda@mail.co.uk”. If it’s genuinely from her email account, then it’s likely she’s been the victim to some malware that’s accessed her email contacts and spammed them all.
That being the case, delete the email without replying or clicking on anything within the body of the email, including images (they can contain malware by themselves), and ideally without even opening it (bit late for that now), then empty/purge your deleted items.
If using a webmail interface via a web browser, you may want to consider deleting the cache and any temporary internet files just to be on the safe side.
If your virus and anti-malware apps are running and coming back clean, then I’d suggest you’re all good to go and nothing to worry about.
