Everyone who says it does not affect the OP, I disagree.
Quantitatively, she has to cover some of pisstaker's duties when she is having stolen time off, so this is extra work, possibly to the detriment of her own work
Quantitatively it affects the morale of the team: when you're working hard and seeing your team-member wilfully slacking for the same reward, it feels bad and encourages resentment, reduces harmony and the good-will needed to make the company run smoothly.
This idea that we should steal time from our employers, just because we can is definitely becoming more prevalent in UK society. We're all protected by laws to stop employer abuse of our time, so why on earth do the wrong thing, just because we "can"?
The pisstaker is no better than a shoplifter, who steals because she "can". When I go to the supermarket, I experience unwanted scrutiny: the doorman, the cameras, the bloody till asking a million times if that's really my own plastic bag. The stupid one way exit path. This is due to people who just take without paying, forcing the rest of us to put up with security measures that we don't need.
People like the OPs work colleague steal from their employer and cause the rest of us to be subjected to infantilising rules at work, like clocking in and out, appraisals, performance management, medical evidence for a rare day off and the withdrawal of working from home, so you can be monitored closely in the office.