Is it normal to be obsessed with your niece?
Depends.It depends
Being crazy about your niece and loving spending time with her can be completely normal. If “obsessed” means sexual or romantic feelings, possessiveness, or difficulty respecting her boundaries, take that seriously and don’t act on it.
If you mean you adore her, think she’s hilarious, and get excited to see her, that’s a very ordinary kind of family love. Lots of aunts and uncles are completely smitten with their nieces.
If you mean a fixation that feels hard to control—or sexual or romantic feelings—the feeling itself doesn’t force you to act, but boundaries matter. Don’t pursue anything or put her in an uncomfortable position; talking it through privately with a therapist can help you keep things safe and clear.