This is correct. So you did change your employer when your wife was in India?
H4 is not based on your employer, rather it is based on your H1B status.
Is her previous H4 I797 still valid? If yes, she can travel using her existing valid H4 visa and I797 however note that CBP will issue her I94 till the expiry of her I797.
Once in the US you will need to file her extension of status based on your new H1B I797.
If her previous H4 I797 has expired, she will need to go for stamping using a copy of your current H1B.