Bloated Daily farts

It's my impression that it's best to limit cucumbers to 1 slice a day depending on the pig. Since your pig is gassy my first guess is the excessive cucumber.

Guinea pigs are unable to pass gas or vomit That's why bloat is so dangerous. A probiotic might be helpful if it's relate to something in her digestive tract. Parsley is high in calcium. I never feed it but if you do, it should only be occasionally. I never feed cucumber since it's gassy. One baby carrot a day should be the limit. There are better choices such as romaine, red and green lettuce, endive, escarole, radicchio. The diet and nutrition chart gives great info on the best foods to feed.

She just got a few days of probiotic, following antibiotics due to bloody urine, so that's checked, I guess.
I very rarely give her lettuce, I know it's also a gassy food. She's a big eater and I'm a bit worried that with only dill, carrots and pepper she's not gonna get enough.

Oh no, lettuce isn't a gassy food and should be offered daily. It makes up the base of my girls' salad. You could use red leaf, green leaf, romaine, etc. The only kind that's unsafe is iceberg, because of the high water content and low amount of nutrients.

I'd cut out the cucumber and see if that fixes it. If not, cut out all the veggies for a day, then start feeding them back one at a time. Wait a couple of days before feeding the next new one. That should help you figure out which one it is.

I'd also cut out the parsley, since she's older. It's high in calcium, and she's probably already getting enough from the pellets. And you might consider giving her some red or green leaf lettuce as a replacement.

Most people limit their cucumber to 1-2 thin slices a day, if not less often.

Also, I'd cut out the parsley, since she's older. It's very high in calcium which can lead so bladder stones, especially in older piggies.

Carrots are high in sugar so a maximum of 1 baby carrot a day.

Lettuce is not gassy at all! It should be a large staple in their diet and given daily. Only iceberg lettuce is not good because it is high in water content and low in nutrients. You might be thinking of cabbage, which would lead to gas and bloat.

Removing the cucumber altogher solved the fart problem from the first day. But I'm not satisfied with her poop, which is like this most of the time in the past 1-2 weeks: (broken link removed)
She never, ever had bowel issues, maybe it's the age. I think the only solution now is to remove all the greens and only keep the hay & pellets, right? But it's so hard to resist her, she obviously wants to eat and is hungry, makes a lot of noise. And at some point (when & how much?) the greens should be gradually reintroduced, I can't just keep her unfed.

Take her off veggies altogether for 24 hours, and see what her poop does. If it hasn't started to firm up, she needs to see a vet, as she may have an intestinal infection. The usual first treatment for such is flagyl (metronidazole), which pigs tolerate very well.

If the poop firms up, start adding veggies back one at a time, with 48 hours in between each new addition. When you hit the one that causes the loose poop, you've found the culprit. Start with just one kind of lettuce, then another, then bell pepper. Those are the staples for pigs, so you begin with them, and then add in the others later.

But go back to the probiotics. They won't hurt, and will likely help. You can use Bene-Bac, or a plain human acidophilus or kyodophilus tablet. Some people have reported good results with Oxbow's digestive support tablet, but those are more pricey than plain probiotics.

Weigh her daily so you'll know whether she's losing weight. If she is, you might want to get some of American Pet Diner's Critter Be Better to supplement her food with. It's got probiotics already in it, and should be good for her.

She pooped last night and the improvements are already showing. Hopefully we won't need a vet. But she's so hungry and displeased that she actually started wheeking, which she does extremely rarely, in critical situations. I hope it's alright if I try to feed her bell pepper a bit later.

You could add grass to her diet. Give small amount as with any new foods & gradually increase. You could include dandelion leaves & flowers 2-3x week for variety.