H4 to H1 Change of Status

Hi Friends,How are you?My spouse is having H4 and currently she is in india. Her H1B petition got approved 10 days back. Her employer is asking her to come to US on H4 and then they will apply for H1 status change. Is it valid? Doesn’t it create any issue?If employer denys to give 1797-B approval notice to her once she comes here on H4, Can’t she switch to any new employer even if she get a good opportunity in future? Does she get locked with this employer if they follow the above process? Does she face issues either with employer or by law?Suppose if she attends H1B stamping interview in india now before coming here and its gets 221g issued or denied, then do they cancel the H4 also?Kindly resolve the above queries with the detailed explanation which will be really helpful for us.