Sorry, I probably wasn't very clear about that!
We had a system whereby we all worked for different teams under a bigger umbrella department (think HR but with different divisions). We all had to cover one colleague for the purposes of sickness/AL/TOIL. I covered her workload and she covered mine.
It was designed so that - broadly speaking - we all provided/received around the same level of cover each for Leave, over the year.
Her workload, like all of ours, was busy but not excessively so & manageable within 9-5 hours. However, she was accruing a huge amount of TOIL which, on top of her AL, meant that my workload was effectively doubled providing cover for her, far more often than other people.
I couldn't understand why, as she wasn't doing anything markedly different to the rest of us and her workload wasn't any bigger.
Our manager (who managed the umbrella section but not the individual workstreams) constantly told me how my colleague was 'snowed under/collapsing under the weight/on their knees' etc and so was forced to come in at 7am just to manage it all.
It was impacting on me quite a bit so I spoke to my colleague and suggested she speak to management about her excessive workload that was impacting on us both. I'd also noticed that the reason management thought she was snowed under was that she walked around from office to office telling everyone that she was snowed under.
That was when she explained that she didn't need to come in at 7am, she just did it so that she could get a lift in to work with her husband. She continued finishing work at 5 as that was when he picked her up. She then just blithely claimed for the extra 2 hours a day.
None of it needed to happen as she had her own car and parking space so could have started at 9am. She just didn't want to (for whatever reason).