Pug died suddenly.

My 8 year old female pug just died. My husband came home from work and she had already passed away. He said her body was hot when he took her out of her crate. The room was not unusually warm and her two brothers (one pug and one westie) were there also and are fine. I came home about 15 minutes later. There was no diahrea, vomit, or blood near her. Her eyes were open and there was a little bit of saliva (not foamy at all) around her gums. Her tongue was blueish purple and was out slightly and her jaws were clenched. I was afraid maybe she choked on her treat I gave her before I left for work about 8 hours earlier. The lady at the crematory did not find anything though. She was overweight, probably obese and we would walk her only on cool mornings. Sometimes she would stop about 3 or 4 houses from ours and just sit there and we'd wait for her to be ready to continue. She's done this for years. We also have a small pool and I would hold her belly and let her paddle. I called it her aqua arobics. We tried to limit her food but after many years of getting her to lose weight we have never been successful. Her behavior leading up to this was completely normal. Panting all the time was normal for her even when it was winter. When it's hot outside we'd dunk her in the pool and she loved it. It would completly curb the panting for a while. She just had surgery to remove a ruptured anal gland 7 months ago and we did all the tests that are recommended to be sure she was healthy enough to proceed with the surgery. If she had heart problems wouldn't that have showed up? I don't think I've ever seen her throwup. Ever. She also had some gall stones removed a while back. Could she have died from their recurrence and us not checking? Also, I'm curious about why my husband felt she was hot. I cut her toenails 2 nights before she died. Could she have gotten an infection from the one I cut too short or even an ifection from anything else? She really didn't start to get cold or stiffen up until we were at the crematory about a hour after my husband found her which makes me wonder if she had just died right before he got home. My pet sitter is also a vet tech at the hospital we take her to and she wondered if it was heart related or maybe an aneurysm. We'll obviously never know for sure but I'm just looking for answers becuase I'm devastated by her death and her health was in my hands and I feel I let her down and gyped her out of a long life. She was a very happy dog. I thought she was healthy as well. She got all her shots she was supposed to get as well as exams. I know any answer you give me will not bring her back but I'm comsumed by this loss and I feel asking questions is the only way I can move forward.
Thank you for your time.
Bonnie

Thank you so much for your time. I appreciate your insight into what happened to Daisy. It really all seems to make sense. She was such a sweet girl and is missed beyond belief. Thanks again.
Bonnie