Came to US(H4)->Went Back->Got H4 stamping again->applying H1 & COS-> Until when can she enter as H4?

Here is the sequence of events and status:

Oct 2014 - Came to US with Stamped H4 (I94 & visa valid till 15 Jan 2015)

Nov 2014 - Filed for H4 extension from US (since H1 extension was approved) - Still Pending

10 Jan 2015 - Left to India for personal Reasons

Feb 2015 - Will be going for interview/stamping H4 for re-entering US (since Primary H1 extension is done)

Now a company is filing her H4 to H1B this year.

Now Her probable date of return is in April-2015(H4). Will this affect anything (since H1 won’t get approved in April… Right ?) ?? Is it compulsory to return to US before 31st March. ??

She is safe to travel on H4 till Oct 2015.

Till Oct 2015, she would be on H4 status even though the new H1 COS petition was filed in April.
If her COS to H1 is approved even before Oct 1st also, she wont be in H1 status(you can verify her H1 approval notice, it would say valid from Oct 1st, 2015 to … in other words, H1 status is valid from 2015 1st Oct.(This entire fact is only for new Quota based H1 petition).