Dear Bea —
Unfortunately, short of a private revelation from God, you cannot know that your loved one is in Heaven. Sometimes people interpret unusual coincidences as "signs" their loved ones are in Heaven, but these are not infallible. A double rainbow appeared on the day of my mother's wake, which all of us took note of.
- Does this mean for sure she's in Heaven?
<I can't say.>
Whether guilt will keep you out of Heaven depends on the gravity of the sin and one's culpability for it.
- If one is guilty of a mortal sin and has not repented of it and (short of the case of "perfect contrition") confessed it, one would be excluded from Heaven.
- For venial sins, these would not keep you from Heaven, even if you did not repent, although you would have to deal with these sins, and the consequences of all your sins in Purgatory after death before entering Heaven.
In short, except for unrepentant serious sins, guilt not dealt with on earth will be dealt with in Purgatory before one goes to Heaven.