Life is a mystery. I’ve heard countless stories of people who made numerous “mistakes” (based on the current HRS guidelines), and their rabbits lived long, happy lives. Other people can do everything right, but if a rabbit is genetically ill, or becomes immuno-compromised, the best care in the world will not make a difference. The first step as I see it is recognizing that Hugo’s passing wasn’t your fault, he would have passed under anyone’s care. You did him a great service by giving him a caring home for his final weeks.
Despite being “prey” animals, the majority of rabbits can be pretty darn resilient. You will always have that occasional rabbit who will go into stasis if looked at wrong, but fortunately, those buns are rare. If it makes you feel better, do a thorough check-up: Blood work, fecals, the whole thing. This will give you an idea of what could be an issue right now or in the near future. Beyond that, stop worrying. Remember, it is more stressful for a rabbit to be taken off to the vet for each individual sneeze or smushy poop. Enjoy every day you have with her… this could be for a year, this could be for 10 years.