Too many ultrasounds?

Had my nit ultrasound and they couldn't see the sex so I went to one of those 4d places at 20 weeks- it's a girl!

Well I'm 27 now and we wanted to see her face so we went back yesterday but she wasn't cooperating and didn't let us get clear pics- the place said we could come back anytime wthjn two weeks to try again - so I am excited and I told my mom- however she is saying why do you keep going, too many ultrasounds are bad for the baby

Is she right?