Shortened: Lucy has a food allergy, although I'm not sure what to. She's been on Hills z/d for well over a year and tolerates it well. We've had a few phases of her going off it, and I worry that if she refuses point blank one of these days, there'll be nothing else to feed her. So this last few months or so, I've tried her on Kattovit Sensitive single-protein (chicken) from Zooplus, on-and-off with the z/d. She seems to like it and I haven't noticed her having any reaction to it. However, I have noticed an increase in booty scooting activity over the last few weeks.
She's flea'd and wormed. As an indoor kitty, I am also in the enviable position of being able to keep tabs on her toilet activity and I have noticed nothing untoward going on (certainly nothing that doesn't belong there). Often they might seem a little small and 'bullety'. She's been an occasional booty scooter since she's been here but not to the extent I'm seeing now. In the last week, I've seen her do it four times. Maybe when I wasn't working from home, I wouldn't have seen her do it, so there's nothing to say that it isn't an ongoing issue.
She always does it post-poop, although she never seems to leave anything behind (sorry if TMI). She's semi-long hair and I had thought it might be because of this... so after one of the last occasions I wrapped her in a towel and unceremoniously gave her a bit of a 'trim' (which she still hasn't forgiven me for).
She is a little overweight... she's maybe 5kg or so and 'short' with it. After a year on steroids for her allergy, and being an indoor kitty, we're still struggling to get the weight off her. This probably means she can't quite reach all the way round to do her housework (although she does clean herself regularly).
Another thing that has struck me, is that she seems to actively seek me out and do it right in front of me (albeit out of arms reach!). Her litter tray is in one of the spare rooms, but she won't do it in there... she'll run either into my bedroom or the living room - wherever I happen to be - and sit down in a bit of a hurry, and off she goes, along the carpet...

I've read that a diet which causes softer poops, can sometimes mean that the anal glands are not exercised when kitties poop, leaving them feeling uncomfortable. Hers don't seem to be like that though. I haven't read too much into any link between constipation and booty scooting however. I did try to sneak some slippery elm bark into her food a few days ago but she wouldn't eat it. I'm limited in what I can give her to eat to disguise it. I have some psyllium husk, but I don't want to make her constipation worse. She doesn't often drink water; I mix her hypoallergenic canned food with warm water to make a soft pate' and she pees fine so I don't think she's dehydrayed.
This is really starting to gross me out. Why might she be doing this? None of the others (4) do it. I've not heard of cats scentmarking or claiming territory in this way.
Before I go shelling out for a carpet cleaner, and/or dragging her off to the vets, what else could I possibly try?
Edited to add: I did read about possible hairballs... she's medium-length haired and is often preening and grooming. I ordered some Gimcat hairball paste to try. I've only just started her on it. Is it worth continuing her on it just in case?
Edited again to add: on a few occasions, I have heard her heaving in the early mornings... I rarely find anything to show why or where however. A couple of times, there's been a wet patch on the carpet. Could this also point to hairballs?