Hi and welcome!
I am very sorry for you loss, but could you please give me a bit more background information?
How old was Emilia and how long have you had her? Was she a single piggy or does she have a companion?
Did she have access to unlimited hay, which should make up to 80% of the daily food intake?
Did she show any signs of illness (hunched up, fluffed up, apathetic, loss of fur and itching, smaller poos or very wet underneath, crackly or very laboured breathing or loss of weight when you were handling her (I don't assume that you have been weighing her regularly)?
Early Signs Of Illness
Guinea pigs can die unexpectly with no previous signs, but without any more information, we are as wise as you as to what has happened.
PS: I am very sorry to say that tanks, no matter how large, are not recommended for keeping guinea pigs in as they don't have good ventilation. This is not a problem when they are used for fish or reptiles that need special heating and need a container that will keep the warmth in. They are also usually not big and wide enough in the first place?