Welcome to the forum!
To add to what others have said, what will happen next is Southeastern will write to your partner saying that they have received a report, have sufficient evidence to prosecute but asking for your comments before deciding how to proceed. It is extremely important that you reply to this letter and you might want to include the following points in your reply:
- That you are sorry for what has happened
- What you have learned from the incident
- That you are keen to settle the matter without the need for court action
- Offer to pay the outstanding fare and the train company's administrative costs in dealing with the matter
Make sure your reply is short and concise, don't give a sob story - they've heard it all before. Southeastern are usually prepared to offer an administrative settlement (commonly known as an out of court settlement) to people who engage with the process and who haven't come to their attention before. There is no guarantee of this and the tthey are within their rights to prosecute you in the magistrates court should they wish to do so.
Be aware that Southeastern will be able to search your online ticket purchase history and if your partner has regularly purchased short tickets to Abbey Wood then you might be asked further questions about this.
If you are offered a settlement you will normally have to pay the outstanding fare at the full Anytime rate with credit given for the fare you did purchase. You will also have to pay an admin fee of around £150. An out of court settlement might appear to be a fine, but it isn't and you won't have a criminal record as a result of accepting one.
Feel free to post a copy of the letter once it arrives (with personal details redacted) along with your draft reply in this thread and forum members will be happy to proof read it for you.