It's not uncommon for her menstrual cycle to be irregular when she first starts. Yes it's normal
My sister is 9 year's old and she started her period like 6 months ago and every month she has her period but like its been 2 or 3 months now and she hasn't had her period yet. Is this normal or should she see a doctor?
its normal so yes.
She sounds normal to me. However if your mom is concerned it is wise to talk to a trusted doctor.